Handling of Fresh Fish
F. B R A M S N A E S
Technological Laboratory, Ministry of Fisheries, Copenhagen, Denmark
I. Introduction 1 II. Keeping Quality of Fish 2
A. Spoilage 2 B. Causes of Spoilage 4
C. Dependence of Keeping Quality on Species, Seasons, and Catch
ing Grounds 5 D. Effect of Catching Methods 8
E. Influence of Temperature 9 III. Handling Fish at Sea 14
A. Fish on Deck 14 B. Delay in Icing 15 C. Evisceration and Removal of Gills 17
D. Washing 19 E. Stowing in the Fish Room 20
IV. Fish Hold Outfitting 25 A. Lining of the Hold and Pen Boards 25
B. Insulation 27 C. Mechanical Refrigeration 29
V. Methods and Rates of Cooling 30
A. Cold Air 30 B. Fresh-Water Ice 31 C. Chilled Fresh Water 34 D. Salt-Water Ice 34 E. Chilled Sea Water or Brine 36
VI. Handling Fish on Shore 40 A. Fish Markets 40 B. Distribution 43 VII. Fish Fillets 49
A. Keeping Quality of Fillets 49
B. Fillet Production 53
References 56
I. Introduction
Current practices in the handling of raw fish are analyzed in the light of results derived from scientific experimentation during recent decades.
M a n y of these results have not yet b e e n fully utilized b y the fish industry in general. O n the other hand, some important findings h a v e already h a d a decisive impact on the routine methods employed in getting t h e fish from the fishing grounds to t h e fishmonger's slab or to the processing plant.
1
This chapter deals particularly with the influence that various meth
ods of handling, environmental conditions, etc., h a v e on the storage life of chilled fresh fish and fresh fillets. T h i s would b e impossible without constantly referring to the action of microorganisms or to the chemical and enzymatic changes taking p l a c e in fish. T h e reader is referred to other chapters in this series, particularly those on microbiology ( V o l u m e I, C h a p t e r 1 4 ) , autolysis ( V o l u m e I, Chapters 12 and 1 6 ) , and nitrog
enous extractives ( V o l u m e I, C h a p t e r 1 1 ) .
Also o f great informative value are t h e m a n y excellent surveys ( R e a y and Shewan, 1 9 4 9 ; Soudan, 1 9 5 0 ; Shewan, 1 9 5 1 ; Borgström, 1 9 5 3 ; Cutting et al, 1 9 5 3 ; Harvey, 1953a, b ; R e a y and Shewan, 1 9 5 3 ; Castell, 1954a;
R i e m a n n and Bramsnaes, 1 9 5 4 ; Tarr, 1 9 5 4 ; M a c C a l l u m , 1955a; B u t l e r et al., 1 9 5 6 ; Ludorff a n d Kreuzer, 1 9 5 6 ) that h a v e b e c o m e available in recent years covering numerous aspects of the handling of fresh fish.
T h e author has only a minor knowledge of t h e methods employed and research carried out b y the important fishing nations ( t h e Soviet U n i o n and J a p a n ) . D e t a i l e d discussions o f the methods employed in the Soviet Union for chilling and icing are available in r e c e n t textbooks (Zaitsev, 1956; Pavlov, 1 9 5 6 ) . A study of m e c h a n i c a l devices for handling, e.g., pumps, conveyors, flumes, etc., has b e e n m a d e b y T e r e n t j e v et al. ( 1 9 5 6 ) .
T h r o u g h o u t this c h a p t e r are references to experimental findings.
D a t a from one set of experiments, carried out with one species o f fish a n d under certain specific conditions, m a y not b e generally applicable.
Studies in r e c e n t years h a v e tended to emphasize that fish show consid
erable variations during their feeding and spawning cycles, and that even the type of food on w h i c h they feed m a y have an effect on their post
mortem spoilage. Moreover, variations in spoiling patterns a n d intrinsic factors from species to species result in differences during storage.
II. Keeping Quality of Fish
A. S P O I L A G E
T h e physical, chemical, and bacteriological characteristics of fish vary with species, seasons, methods of catching, fishing grounds, etc. None
theless it is possible to give the following general description of the changes that take place during decomposition after death, eventually leading to totally spoiled fish, unfit for human consumption ( R e a y and Shewan, 1 9 4 9 ) .
F r e s h l y caught fish have a shining, iridescent surface covered with a nearly transparent, uniformly and thinly spread slime. T h e eyes are protruding, bright, with a jet b l a c k pupil and transparent cornea. T h e gills are generally b r i g h t a n d free from visible slime. T h e flesh is soft and flabby, tending to retain finger indentations. Soon after death, how-
ever, w h e n the b o d y stiffens (rigor m o r t i s ) , the flesh b e c o m e s hard, firm, and elastic and does not readily yield juice under pressure.
T h e odor of the flesh is generally described as "marine," "fresh sea- weedy," or "laky" (for fresh-water fish). T h e flesh of fatty fish has, in addition, a pleasant, oily, margarine-like odor.
As the fish spoils and finally b e c o m e s putrid, the surface loses its bright sheen and color and b e c o m e s covered with a thicker slime, w h i c h grows increasingly turbid and lumpy. Finally, the color of the slime b e comes yellow or brown. T h e eyes gradually sink and shrink, t h e pupil b e c o m i n g cloudy and milky and the cornea opaque. At first the gills assume a bleached, light pink color that finally turns to greyish brown, at which point they b e c o m e covered with a thick slime. T h e flesh gradu
ally softens until it is very easily stripped from the b a c k b o n e and exudes juice under light pressure. Simultaneously the elasticity disappears. Dur
ing this breakdown, the flesh changes from its original translucent sheen to a dull, milky appearance. I f originally colored, as in salmon, the tint often fades to greyish yellow. Along the b a c k b o n e above t h e belly and spreading b a c k toward the tail, a reddish brown discoloration penetrates from the main blood vessel into the flesh.
Newly caught fish generally carry feed in their digestive tracts. I f they are not gutted soon after being caught, the powerful digestive en
zymes attack the viscera and belly walls, causing discoloration—so-called
"belly-burn"—or disruption, giving rise to so-called "torn bellies." T h e latter phenomenon can occur in the course of a few days at ice tempera
ture, even if the digestive tract is nearly empty, but m u c h more rapidly in the case of feeding fish. I t is a well-known fact that with pelagic, fish like herring, and sprat, "feedy" fish (i.e., very full of f o o d ) , m a y develop torn bellies long before other signs of spoilage set in.
As spoilage proceeds there is a gradual c h a n g e in odor of the raw fish. Initially it is fresh; it then b e c o m e s "sweetish," sometimes "fruity";
later, "ammoniacal" or "fishy" odors dominate, until finally the well- known putrefaction odors b e c o m e evident.
W h e n cooked, very fresh fish exhibit delicate, pleasant odors and flavors. As spoilage proceeds, these odors and flavors generally b e c o m e first "flat" and uninteresting ( a situation which, in iced white fish, lasts several d a y s ) , then "fishy," before the putrid flavors begin.
T h e limit of edibility in white fish usually occurs w h e n the odor con
sists of a mixture of "ammoniacal" ( a m m o n i a , trimethylamine [ T M A ] , and other a m i n e s ) and putrid elements ( H2S , indole, e t c . ) .
I n F i g . 1 are shown the organoleptical, chemical, and bacteriological changes in haddocks that have b e e n carefully gutted, washed, and stowed in plenty of ice.
I n fatty fish, an oily and later a rancid taste adds to the picture. At low temperatures ( 0 - 2 ° C . / 3 2 - 3 60 F . ) this rancidity m a y develop so rapidly that the rancid flavor b e c o m e s the limiting factor of keeping quality (Sigurdsson, 1 9 4 7 ) .
B . C A U S E S O F S P O I L A G E
T o o little knowledge is available on the slight yet important changes in appearance, odor, and flavor that take place in raw fish during the first few days of storage.
Storage time in ice (days)
Organoleptic changes No marked spoilage.
9 10 11 12 13 14 15 16 17 18 19 20 Pirns e II
F i r s t definite signs of spoilage, softer flesh, staler a p pearance, strength
ening of odor.
Phase III Definite stale appearance and odor, and soft
flesh.
Phase IV Rapid deterioration
from staleness to putridity.
Storage time in ice (days)
Chemical changes
2 3
Dimethylamine i n c r e a s e s steadily.
9 10 11 12" 13 14 15 16 17 18 19 20
Trimethylamine i n c r e a s e s rapidly.
Ammonia i n c r e a s e s rapidly.
Storage time in ice (days) Changes in bacterial numbers
0 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 17 18 19 20 Bacterial numbers rapidly increase.
FIG. 1. Diagram showing side by side the organoleptic, chemical, and bacterio
logical changes in haddocks, carefully gutted and washed and stowed in plenty of ice (Cutting et al, 1 9 5 3 ) .
A great deal of valuable work has b e e n done on the biochemical post-mortem changes in lipids, muscle extractives, etc. Most of this work has b e e n carried out without direct relation to the quality of the fish.
T h e r e is, however, similar research in progress w h e r e the workers are thinking in terms of quality. As an example, the reader is referred to the work b y S h e w a n and J o n e s ( 1 9 5 7 ) and to several later publications b y these and other authors.
T h e more extensive changes previously described have three main groups of causes: ( 1 ) bacteria; ( 2 ) digestive enzymes; and ( 3 ) others (e.g., oxidation leading to r a n c i d i t y ) .
T h e relative importance of these causes varies with the species of fish. It is therefore common to distinguish b e t w e e n white fish ( c o d and related species) and flatfishes, w h i c h are economically the most impor
tant, and the so-called fatty fish ( s u c h as herring, mackerel, sprat, tuna, salmon, and t r o u t ) , which contain a considerable amount of fish oil in the flesh during the greater part of the year.
White fish have a negligible oil content in the flesh and rancidity is
therefore not a serious problem during cold storage. Furthermore, these species are generally gutted soon after capture. T h e digestive juices re
moved with the guts consequently have little opportunity to contribute to spoilage. T h i s explains w h y bacterial activity is b y far the most im
portant spoilage factor in this kind of fish. Attempts to m a k e this fish keep as long as possible are directed toward checking or eliminating t h e bacteria c o n c e r n e d ( s e e V o l u m e I, C h a p t e r 1 4 ) .
Fish-spoiling microflora is found in the external slime. I n contrast, the flesh of the fish w h e n caught is sterile. Moreover, bacteria are present in the digestive tracts of feeding fish, whereas the tracts of fasting fish frequently are empty or at the most have a low microbial count.
It is generally a c c e p t e d that the bacterial spoilage of the flesh does not b e g i n until rigor mortis has b e e n resolved, b e c a u s e t h e p H during rigor is less conducive to bacterial growth. T h e longer the rigor lasts, the better the keeping quality of most terrestrial animals ( M a d s e n , 1 9 4 3 - 1944; Ingram, 1 9 4 8 ) . Results from examinations of the duration of rigor as related to p H in various fishes tend to coincide with the general ex
perience of fishermen. T h e amount of glycogen in fish muscle just after death and the amount of lactic acid formed during rigor are not nearly as great as in mammals ( s e e V o l u m e I, p. 4 0 3 ) . I n haddock, whiting, and related species, t h e ultimate p H , w h e n rigor is at maximum, is normally 6.2-6.6 ( R e a y and Shewan, 1 9 4 9 ) . E v e n at this level t h e growth o f orga
nisms mainly responsible for fish spoilage appears to b e effectively checked. Consequently, from the point of view of keeping quality, rigor in fish should last as long as possible.
I n fatty fish all three above-mentioned groups of causes play a part.
Belly burn brought about b y juices in the digestive tract has already been mentioned. This enzymatic breakdown is quite c o m m o n with small pelagic fish such as herring, sprat, and mackerel, which in most cases are left ungutted b e c a u s e of the large amount of labor involved in gutting.
C h a n g e s in fish oils normally grouped under "oiliness" and "rancidity"
are also important causes of spoilage. As mentioned earlier, rancidity may b e the limiting factor of keeping quality. T h i s is claimed to b e the case in general for gutted fatty fish ( B r a m s n a e s and Hansen, 1 9 6 2 ) . T h e r e is, however, no widespread agreement on this point.
C. D E P E N D E N C E O F K E E P I N G Q U A L I T Y ON S P E C I E S , S E A S O N S , AND C A T C H I N G G R O U N D S
T h e fishing industry knows that some species of fish k e e p b e t t e r than others and that some m a y even detrimentally affect the keeping proper
ties of other species stored with t h e m ( s e e Section Ι Π , Ε ) .
T h e onset and duration of rigor mortis vary with the species; this
fact m a y explain some of the differences in keeping quality. Cutting ( 1 9 4 9 a ) examined various species from one hour's haul on inshore ground. T h e fish w e r e allowed to struggle on deck. T h e time in i c e b e tween hauling and t h e termination of rigor mortis varied as follows:
Whiting, 2 1 hr.; cod, 4 0 hr.; plaice ( a t 1 6 ° C . / 6 0 . 8 ° F . ) , 4 4 hr. Flatfish normally have a b e t t e r keeping quality than gadoids, such as cod.
Messtorff ( 1 9 5 4 ) found that at 0 ° C . / 3 2 ° F . rigor mortis lasted 8 3 hr.
in cod and 1 2 0 hr. in o c e a n perch. ( F o r further on rigor, see Section Ι Ι , Ε ; also V o l u m e I, C h a p t e r 1 2 ) .
T h e r e are no exact data that show the possible correlation b e t w e e n duration of rigor and the level of ultimate p H in different species of fish.
Halibut is known to have a long period of rigor and to b e one of t h e best keeping fish. Hjorth-Hansen ( 1 9 4 3 ) , measuring p H in some speci
mens of this fish kept in ice, found the lowest p H to b e 5.57 about 1 1 days after death. I n c o d h e found ultimate p H values about 6.30. Tomlinson et al. ( 1 9 6 1 ) found with trout and flounders that the longer lactic acid continues to b e p r o d u c e d after death, the longer the time before rigor is resolved.
I t is extremely difficult and hazardous to state absolute values for the storage life of different species, since these vary very m u c h with methods of handling, season, etc. W h i t e fish and some elasmobranchs with heads on and gills intact w e r e caught in the North Atlantic and adjacent waters, handled according to existing good practice, and stowed in a hold with plenty of ice. T h e following tabulation m a y serve to indi
c a t e their maximum limits of edibility. I t is necessary to r e a c h port well ahead of these limits to ensure sufficient time for distribution.
Storage life
Fish (days)
Cod 12 Whiting 9 Hake 15 Plaice 18 Dab 12 Halibut 21 Ray, skate 12 Porbeagle (herring shark) 21
Storage life of iced fish in boxes on shore will often b e found to b e m u c h shorter than the values given above. D u r i n g the summer season, fish often have a shorter storage life than at other seasons. S h e w a n ( 1 9 5 8 ) has recorded that for cod landed in E n g l a n d there appear to b e three p e a k periods of relatively low keeping quality during the year. T h e first, in spring, m a y b e related to some biological factor, such as spawning;
the second, to t h e higher temperature prevailing during midsummer. So far no explanation has b e e n forthcoming for the last peak, in O c t o b e r .
Castell et al. ( 1 9 5 9 b ) and Castell and Giles ( 1 9 6 1 ) also found sea
sonal fluctuations in Atlantic c o d and haddock. Differences in keeping quality of c o d b e t w e e n catches from various fishing grounds were found b y E h r e n b u r g and S h e w a n ( 1 9 5 5 ) ; see F i g . 2.
10
k 8 12 16 20 24 DAYS IN I C E
FIG. 2 . Flavor scores of North Sea, Lofoten, and Spitzbergen fish plotted as batch means against days in ice (Ehrenburg and Shewan, 1 9 5 5 ) .
W h e n it comes to pelagic fish the picture is not at all clear. At t h e F o o d and Agriculture Organization meeting in 1 9 5 0 on " T h e T e c h n o l o g y of Herring Utilization," storage life in i c e from about 2 days for Scottish summer herring to about 12 days for Norwegian winter herring were indicated.
Occasionally, unknown environmental conditions in certain fishing grounds greatly affect the quality of the fish, and fishermen must either move to other banks or risk taking a loss in their catch. So-called "milky"
or ' chalky" hake exhibiting an unusual degree of softness that renders them quite unsuitable for normal trade uses, have b e e n particularly in
vestigated. W h e n this condition is at its worse, the muscle of the fish is completely broken down as if b y digestion and has the appearance and texture of thick, milky-white paste. T h i s phenomenon, w h i c h does not coincide with a greater bacterial spoilage, is believed to b e caused b y spores of the parasitic protozoon Chloromyxum thyrsites. T h i s calamity occurs particularly in fish landed in South African, Australian, and South English ports ( F l e t c h e r et al, 1 9 5 1 ) .
Another example is the "jellied" American plaice, w h i c h occurs on
the Grand B a n k among mature females, particularly in areas of low bottom temperatures ( s e e further V o l u m e I I , C h a p t e r 2A, p. 3 7 ) . L o v e
( 1 9 6 1 ) reports on "jellied" flounder from t h e Gulf o f M e x i c o a n d gives a survey of similar findings in various parts of the world.
D . E F F E C T O F C A T C H I N G M E T H O D S
It is generally assumed that the m o r e exhausted a fish is when it dies, the lower the muscular reserves of glycogen and the smaller the drop in p H , though there appear to b e no data showing such a correlation. F o r domestic animals, however, parallel data are available ( C a l l o w and Ingram, 1 9 5 5 ) .
3 0 0
1 0 0
ο c
ι ι
ι J J 1— ιQ U 8 12 16 2 0 2 4 2 8 T i m e ( h o u r s )
FIG. 3. Rigor curves for haddock caught by hand-line (top curve) and by trawl (bottom curve). Fish were tied to a board; board and fish were immersed in sea water; a thread was tied around the tail fin and led up over two pulleys to a scale pan. The weight necessary to cause a pointer attached to the thread to move through a fixed distance was determined at intervals (Leim et al., 1927).
I t is also generally recognized that catching methods influence the level of initial glycogen. E w a r t ( 1 8 8 7 ) found that whereas rigor m a y persist as long or nearly as long in some trawled fish as in fish caught b y line, in most cases it disappears sooner from trawled fish. H e concluded that as a rule putrefaction sets in more quickly in the former than in the latter fish, provided that t h e line-caught fish are slaughtered and gutted as soon as they leave t h e water. T h e same results would most p r o b a b l y have b e e n obtained i f the fish h a d b e e n merely slaughtered without gutting, or simply stunned.
Anderson ( 1 9 0 7 ) examined m a n y lots of fish taken from trawls and hand-lines and observed that rigor mortis set in earlier and disappeared
earlier in trawled fish. H e attributed this to struggling, crushing, and anoxemia.
T h e s e differences, as found b y L e i m et al. ( 1 9 2 7 ) , are shown in F i g . 3. T h e s e authors also measured the glycogen content of haddock caught with hand-lines at about 0 . 1 2 % a n d at almost 0 % in trawled fish.
T h e s e results are often looked upon as b e i n g of merely a c a d e m i c in
terest for salt-water fishing. O n t h e other hand, they seem to show what has always b e e n a c c e p t e d as true b y fishermen, but never sufficiently proven, namely that: ( 1 ) the shorter a trawler haul is, the better the fish will keep; and ( 2 ) fish arriving alive over the rail should b e slaugh
tered or stunned immediately.
W h e n handling fresh-water fish, particularly fish cultivated in ponds, one has a better possibility of choosing the right treatment before death in order to reap t h e m a x i m u m keeping quality of fresh fish. T h e type of food that the fish ingests during the last days of its life m a y also play a role, as is the case with domestic animals.
E . I N F L U E N C E O F T E M P E R A T U R E
T h e beneficial effect of reduced storage temperature on the keeping quality of fish has long b e e n established. E w a r t ( 1 8 8 7 ) , studying trout, found that as the temperature was lowered rigor mortis was later in making its appearance. At 3 0 ° C . / 8 6 ° F . , rigor set in about 5 minutes after death in fish that h a d b e e n allowed to die naturally; this t i m e increased to 3 0 - 4 0 hr. at — 1 ° C . / 3 0 ° F . H e also found considerable individual differ
ences. Cutting ( 1 9 4 9 a ) examined various white fishes, among w h i c h w e r e cod, haddock, whiting, and lemon sole; the fish w e r e not stunned, b u t were allowed to struggle without interference. I n some instances h e found that icing immediately after the fish w e r e caught did not affect the r a t e at w h i c h rigor sets in c o m p a r e d with storage in air ( 1 2 - 1 6 ° C . / 5 4 - 6 1 ° F . ) . W i t h other species he recorded periods of only 2 - 3 hours at 0 ° C . / 3 2 ° F , against 1-2 hours at l l - 1 6 ° C . / 5 2 - 6 1 ° F .
This apparent conflict b e t w e e n results, perhaps t h e result of differ
ences in species, is of minor importance c o m p a r e d with the fact, recorded b y the workers mentioned above and b y others ( S c h l i e , 1 9 3 4 ; Messtorff, 1 9 5 4 ) , that the resolution of rigor mortis, a n d h e n c e the onset of bacterial attack, is delayed b y chilling t h e fish in ice. Cutting found that the time b e t w e e n hauling and t h e end of rigor for cod kept in ice or in air at 1 1 ° C . / 5 2 ° F . was 4 0 and 3 0 hr., respectively. F o r whiting the correspond
ing figures w e r e 2 1 and 12 hr. Messtorff ( 1 9 5 4 ) found for ocean perch 126 and 9 7 hr., respectively. ( F o r further data on rigor mortis in fish, see V o l u m e I, C h a p t e r 12; also Section I I , C , this c h a p t e r . )
T h e influence of temperature on the growth of bacteria of the fish-
spoiling type is considerable, and the growth is markedly curtailed b y small decreases in the range: — 1 ° C . / 3 0 ° F . to 5 ° C . / 4 1 ° F .
Similar information has b e e n acquired b y examining changes in the fish itself. B e c a u s e bacteria play the greatest role in t h e spoilage of "wet"
white fish, these species have b e e n the main objects of such research.
Hess ( 1 9 3 2 ) m a d e a thorough study of the influence of temperature within the range of — 1 . 1 ° C . / 3 0 ° F . to 2 . 2 ° C . / 3 6 ° F . H e studied haddock
I 1 1 ι ι ι I
2 U 6 8 10
D a y s
FIG. 4. Volatile basic nitrogen in haddock muscle emulsion through autolytic plus bacterial decomposition (Hess, 1932).
muscle extracts and emulsions, together with a few h e a d e d and gutted fish. T h e yardstick for decomposition was total volatile basic nitrogen
( T V B ) ; his findings in muscle emulsion are shown in F i g . 4 .
Calculating t h e temperature coefficient ( Q i o ) for the interval, 2 . 20C . / 3 6 ° F . to 1 . 10C . / 3 4 ° F . , values b e t w e e n 2.2 and 12.7 w e r e found, while the values for the range 0 ° C . / 3 2 ° F . to — 1 . 1 ° C . / 3 0 ° F . were m u c h higher (ranging from 7 to several t h o u s a n d ) . T h e extreme high values, h e explained, w e r e the result of no measurable increase of b a c t e r i a in t h e muscles during the first days of storage.
Hess concluded that a lowering of temperature b e c o m e s more and more effective in retarding bacterial decomposition in t h e lower tempera
ture range. Several years elapsed before similar experiments w e r e again carried out, but this time they w e r e on a m o r e extensive scale and under typical commercial conditions. Heiss and Cursiefen ( 1 9 3 8 ) , using eutec-
tic i c e s — o n e with N a2H P 04 with a melting point o f — 0 . 9 ° C . / 3 0 . 4 ° F .
— o b s e r v e d that fresh herring so stored k e p t b e t t e r than in ordinary ice.
British experiments on the handling a n d stowage of summer herring showed that temperature was b y far the most important factor influenc
ing preservation ( R e a y and Shewan, 1 9 5 3 ) . I n herring kept without ice at 1 0 ° C . / 5 0 ° F . to 1 5 ° C . / 5 9 ° F . , the production of trimethylamine ( T M A ) , starting with a b o u t 1 mg. T M A - N per 1 0 0 ml. juice, was generally slow during the first day giving figures b e t w e e n 2 and 4 mg. ( T M A - N ) . B y the end of the second day, however, the levels lay b e t w e e n 2 0 a n d 4 0 mg. T M A - N . I n fish k e p t in plenty of i c e there was only a slight rise in T M A , up to 2 - 3 mg. T M A - N , even after 1 0 0 hours. Sigurdssons ( 1 9 4 7 ) results with herring closely agree; h e observed a sharp rise in T M A after only 1 day at 1 0 ° C . / 5 0 ° F . , b u t after 4 days at 0 ° C . / 3 2 ° F .
R e a y and S h e w a n , using sensory assessment of quality, found that herring kept at ordinary temperatures, 1 0 - 1 5 ° C . / 5 0 - 5 9 ° F . , had, on an average, passed a m i n i m u m standard of freshness 9 hr. after catching, as opposed to 3 2 hr. for adequately i c e d fish. T h e standard, difficult to de
scribe, was that the fish "have lost no m o r e than little of their fresh marine' or 'seaweedy' quality and have developed only a slight b u t still quite sweet 'oiliness' in b o t h odor a n d flavor." T h i s point was r e a c h e d long before the above-mentioned sharp increase in T M A content.
Castell a n d M a c C a l l u m ( 1 9 5 0 ) stored fresh m a r k e t c o d a n d deter
mined the keeping time as the m e a n time required for the middle muscle to r e a c h the spoilage threshold of 15 mg. T M A - N per 1 0 0 g. fish with the following results.
Storage temperature Keeping time
( ° C ) ( ° F . ) (days)
0 32 8.0
3 37.4 4.3
10 50 1.5
E x p e r i m e n t i n g with fillets o f c o d a n d h a d d o c k c u t from normal quality fish in a local plant in Halifax, Castell and M a c C a l l u m also found that a reduction in storage temperature o f 3 degrees immediately a b o v e freezing adds proportionally far m o r e to t h e keeping time than a greater reduction at a higher temperature. A decrease in t e m p e r a t u r e from 2 . 8 ° C . to — 0 . 3 ° C . / 3 7 ° F . to 3 1 . 5 ° F . approximately doubled the keeping time as judged b y the development of T M A .
I t is interesting to see that somewhat similar results w e r e obtained b y D y e r a n d D y e r ( 1 9 4 9 ) , using a taste panel. T h e y observed that fillets cut from fish still in rigor b e c a m e u n a c c e p t a b l e after 3 days' storage at 5 ° C . / 4 1 ° F . , and after 8 days at 0 ° C . / 3 2 ° F .
F r o m British experiments, Cutting et al. ( 1 9 5 3 ) conclude that cod spoil about 2y2 times as fast at 4 . 4 ° C . / 4 0 ° F . and about 5τ/2 times as fast at 1 0 ° C . / 5 0 ° F . as they do at 0 ° C . / 3 2 ° F . I f the fish are m e d i u m or large trawler c o d with a period of keeping quality of about 14 days at 0 ° C . / 3 2 ° F . , t h e data in T a b l e I will give an idea of t h e storage life expected at the other temperatures.
TABLE I
STORAGE L I F E OF A LOAD OF W E L L HANDLED COD AT VARIOUS TEMPERATURES0
Storage (°C.)
temperature ( ° F . )
Storage life (days)
Temperature interval
(°C.)
Average difference in storage life (days per °C.)
0 32 14
0-4.4 1.9
4.4 40 5y2
4.4-10 0.5
10 50 zy2
a From Cutting et al. (1953).
Hansen ( 1 9 6 0 a ) , in one of his experiments with small cod stored in still air at — 1 . 3 ° C . / 2 9 . 7 ° F . , 0 . 6 ° C . / 3 3 . 1 ° F . , and 3 . 5 ° C . / 3 8 . 3 ° F . , finds keeping times of 16, 11.9, and 8.6 days, respectively. F o r plaice, one ex
periment resulted in 13.1, 11.3, and 7.0 days' keeping quality at — 0 . 6 ° C . / 3 0 . 9 ° F . , 0 . 6 ° C . / 3 3 . 1 ° F . , and 5 . 3 ° C . / 4 1 . 5 ° F . Not b e i n g stored in ice, the fish could not profit from the normal leaching effect ( s e e S e c t i o n V , A ) of melting water. Plaice, particularly, would generally k e e p longer than 13 days at — 0 . 6 ° C . / 3 3 . 1 ° F . I n the experiment with cod, the differences in keeping quality per degree centigrade for the two intervals w e r e cal
culated at 2.5 and 1.1 days. T h e corresponding figures for plaice w e r e 1.5 and 0.9 days.
B y measuring T V B a n d t h e electric resistance of t h e fish muscle, it has b e e n recorded ( L u d o r f f and Kreuzer, 1 9 5 6 ) that haddock and c o d stored at 3 ° C . / 3 7 . 4 ° F . h a d lost the same in freshness after 3 - 4 days as had fish stored at 0 ° C . / 3 2 ° F . ( i n i c e ) after 9 days.
A m o n g later results with fatty fish, those of B y s t e d t ( 1 9 5 3 ) should b e mentioned. B y taste panel assessment of mackerel, one lot stored in ice at 0 ° C . / 3 2 ° F . and the other in air at 5 ° C . / 4 1 ° F . , h e found that t h e same loss in quality of ungutted fish h a d occurred in 5 days at 5 ° C . / 4 1 ° F . as in 9 days at 0 ° C . / 3 2 ° F . F o r the gutted and c l e a n e d fish the figures were 5 and 7 days, the smaller difference here b e i n g due to the fact that rancidity was m u c h m o r e pronounced in the gutted than in the round fish at 0 ° C . / 3 2 ° F . , whereas this was not the case at 5 ° C . / 4 1 ° F .
A characteristic feature of most salt-water fish is the psychrophilic nature of the surface flora of the fish ( H e s s , 1 9 3 2 , 1 9 3 4 ; D y e r , 1947-1950;
Castell and M a p p l e b e c k , 1 9 5 2 - 1 9 5 3 ) . T h i s necessitates efficient chilling t o c h e c k microbial growth ( C a s t e l l a n d M a c C a l l u m , 1 9 5 0 ) . I c i n g
and salt-water cooling are alternative ways of accomplishing this goal.
T h e contaminating flora in icing-dressing and storage plants also tend to b e psychrophilic ( C a s t e l l et al, 1 9 5 9 a ) ; see further V o l u m e I, C h a p ter 14.
In summary, whereas storage at around 5 ° C . / 4 1 ° F . for most foods is almost as good as storage at ice temperatures, since most b a c t e r i a pres
ent on t h e m do not grow at either temperature, this does not hold true in t h e case of fish. J u d g i n g from scientific studies of microorganisms as well as from t h e m o r e crude experiments on b o a r d trawlers or on a pilot scale ashore, it has b e e n demonstrated that the keeping quality of chilled fish is greatly influenced b y the temperature. Results seem to indicate that this influence is m o r e pronounced for white fish than for fatty fish.
T h e r e has b e e n a certain interest in keeping fresh fish at a few degrees b e l o w the freezing point, so-called subfreezing. Golovkin and Pershina
( 1 9 5 8 ) , continuing some earlier Russian experiments, stored pickerel at
— 2 . 6 ° C . for 2 9 days and found that t h e storage life was prolonged com
pared with that of t h e same fish kept in ice. T h e laboratory experiments w e r e confirmed b y field tests. T h e authors found that an undesirable factor in this m e t h o d of refrigerated treatment is the somewhat lower water-retaining property o f subfrozen tissue in comparison with those of chilled specimens.
I n D a n i s h experiments, codling w e r e stored at — / 4 ° C , — 4 ° C , and
— 8 ° C . T h e fish at — 4 ° C . altered in bacterial, chemical, and flavor prop
erties in t h e same w a y as those at — / 4 ° C , b u t considerably m o r e slowly, so that the storage life was about t w i c e as long. T h e r e was no increase in the bacterial count on t h e fish at — 8 ° C , b u t a slight increase in t h e volatile b a s e content was observed (Anonymous, 1 9 5 8 b ) .
In later experiments, codling w e r e stored at — 4 ° C . and — 2 ° C . A great difference in t h e bacterial growth was found b e t w e e n t h e two groups, in that t h e — 4 ° C . group did not r e a c h about 1 million b a c t e r i a per gram until after 3 - 4 w e e k s ' storage. However, no obvious difference was found b e t w e e n t h e two groups in flavor and texture. T h e texture, in particular, s e e m e d in b o t h cases to b e adversely influenced b y the partial freezing. Therefore, although no putrefaction occurred, the fish was judged n o n a c c e p t a b l e b y the taste panel after 3 weeks' storage ( A n o n y mous, 1 9 6 0 a ) .
Similar British experiments showed that although the fish was judged still edible after m o r e than a m o n t h at — 3 ° C , slow spoilage did t a k e p l a c e and in a n y case the flesh was extensively softened b y the freezing
(Anonymous, 1 9 6 1 ) .
III. Handling Fish at Sea
E v e r since i c e was introduced on b o a r d ships for preservation of fish in the latter part of the 19th century, skippers a n d ship owners h a v e gradually improved the methods of preservation and t h e construction and outfitting of their boats. T h e progress has b e e n due, to a considerable extent, to application of results obtained in scientific laboratories a n d at experimental stations.
T h e very difficult conditions—gales, high seas, and ice-cold w e a t h e r
—under w h i c h the work on b o a r d a fishing vessel often has to b e carried out must b e b o r n e in mind. Improvements in handling that look simple on land, therefore, m a y not b e easy to introduce at sea. Nevertheless, the fishing industry will listen with interest to anyone w h o c a n point out possibilities for further improving the quality of fresh fish landed.
R e s e a r c h work in G r e a t Britain, particularly during the 1920's and 1930's showed that the factors that chiefly influence the quality of fish at landing are ( a ) temperature, involving the proper use of ice on board ship; ( b ) care and cleanliness of handling on d e c k and in t h e hold, and ( c ) distance from the fishing grounds.
L u m l e y et al. ( 1 9 2 9 ) m a d e experiments on b o a r d t w o large trawlers that h a d b e e n e q u i p p e d with washing tanks or troughs of steel, fish shelves of galvanized iron, hot w a t e r for cleaning, and a tank for steriliz
ing implements and shelves. This, together with a careful handling and proper chilling of the fish, resulted in considerable improvement in quality, so that fish 1 0 - 1 2 days in ice on landing w e r e sometimes rated b y a panel of fish merchants and vessel owners as b e i n g at " 5 - 6 days caught." Cor
responding improvements w e r e obtained on shorter trips.
However, quantitative data on the relative practical importance of each of the factors influencing the quality of fish did not really appear until after 1 9 5 0 .
A . F I S H ON D E C K
W h e n taken over the rail, fish are generally d u m p e d or thrown into enclosures (so-called pounds, checkers, bins, or p e n s ) on the deck. In large vessels, fish are kept in the pounds until they are either eviscerated or taken whole under deck. In small boats ( u p to 1 0 0 ft.) it is usually possible to transfer the fish immediately from the deck into boxes or baskets so that they are not d a m a g e d b y b e i n g r u b b e d against the deck or against each other b y the movements of the boat. W h e n dealing with fish that are to b e b l e d before eviscerating, it is r e c o m m e n d e d that cutting of the throat b e done on a grate from w h i c h chutes lead to bleeding bins w h e r e the fish stay for at least 15 minutes before b e i n g gutted ( G r a h l , 1 9 5 1 ) .
Severe bruising and d a m a g e of freshly caught live fish usually re
sult in extravasation and consequent discoloration of t h e flesh. Bruising of d e a d fish does not always produce discoloration. I t is generally as
sumed that such fish have a shorter keeping time than u n d a m a g e d fish.
This has n o w b e e n demonstrated experimentally ( C a s t e l l et al., 1 9 5 6 ) . After 6 days in i c e , bruised fish w e r e worse in odor and T M A content than the u n d a m a g e d control fish.
R e a y and S h e w a n ( 1 9 5 3 ) reported experiments with summer herring.
F i s h p a c k e d into boxes straight from the net and thereafter left undis
turbed w e r e noticeably superior to fish taken from bulked lots and p a c k e d in shore boxes at landing.
B . D E L A Y I N I C I N G
I t is not surprising that storage on the d e c k for a few hours without ice, especially in t h e sunlight, m a y increase t h e temperature of t h e fish considerably. F o r South African fish, Dreosti ( 1 9 4 9 ) reported rises from 1 2 - 1 5 ° C . / 5 4 - 5 9 ° F . to a b o u t 2 7 ° C . / 8 0 ° F . in less than 2 hr. T h i s is un
questionably a crucial p r o b l e m in all tropical areas. Russian reports from a large-scale fishing expedition outside Dakar, W e s t Africa, indicated that sardines left on d e c k r e a c h e d inedibility within about 2 hr. ( T e r e n t j e v a , 1 9 5 8 ) .
I t is also interesting to note that even in winter there is a considerable adverse effect on keeping time w h e n fish lie on deck. E x p e r i m e n t s in w h i c h white fish w e r e exposed to 7 ° C . / 4 5 ° F . for 18 hr. before packing in i c e showed that t h e a v e r a g e storage life was r e d u c e d b y 2 days as c o m p a r e d with controls i c e d immediately after c a t c h i n g ( C u t t i n g et al., 1 9 5 3 ) . S u c h a delay m a y well o c c u r on b o a r d large trawlers, and per
haps even m o r e often on small coastal fishing craft that do not take i c e on b o a r d in t h e autumn and winter seasons.
TABLE I I
TRIMETHYLAMINE AND pH VALUES OF COD FILLETS FROM FISH AFTER EXPOSURE TO VARIOUS CONDITIONS'1
Hours Sun
Air temper
ature
Days in hold in plenty
of ice
Trimethylamine
(TMA) pH
exposed shine
Air temper
ature
Days in hold in plenty
of ice Exposed Controls0 Exposed Controls0
2
+
5°C. 3 0.40 0.38 6.5 6.57 — 3-5°C. 7 0.85 0.91 6.7 6.6
3
+
15°C. 5 1.30 0.66 6.8 6.75
+
15°C. 5 1.19 0.55 6.7 6.5a From Castell et al. (1956).
0 Values for cod caught at the same time but not exposed on the deck before icing.
Castell et al. ( 1 9 5 6 ) examined fish from the top of a pile on the deck.
( T a b l e I I shows the results, as well as comparison with unexposed fish.) I n cool weather, 2 and 7 hours' exposure had no perceptible effect on the fish kept afterwards in i c e for 3 and 7 days before filleting. O n the other hand, exposure for 3 and 5 hr. at 1 5 ° C . / 5 9 ° F . resulted in inferior quality
FIG. 5. Washing apparatus in use on board a British trawler. (By courtesy of the Torry Research Station, Aberdeen; British Crown Copyright.)
after 5 days in ice. It should b e noted that the storage experiments were not carried b e y o n d 3 to 7 days.
In order to speed up the handling of fish on d e c k it is a c o m m o n practice, with pelagic fishes such as herring, to use bunker holes on t h e d e c k and chutes to m o v e the fish rapidly b e l o w deck. O t h e r fish are most often collected first in baskets for gutting and cleaning and are then brought under deck. T h i s takes time, and the trawler d e c k flume
that has b e e n devised in South Africa is possibly an a c c e p t a b l e solution.
I t is claimed that t h e time b e t w e e n release of the cod-end and the lower
ing of the gutted and h e a d e d fish into t h e hold has b e e n halved ( B r a m s - naes, 1 9 5 7 ) . Another interesting apparatus in this respect is the British washing m a c h i n e for large trawlers shown in F i g . 5. E x p e r i e n c e on b o a r d commercial vessels shows that b y t h e use o f t h e washing machines fish c o m e down into t h e hold in a m u c h m o r e even flow, and consequently there is time for t h e m to b e m o r e carefully stowed and i c e d than pre
viously, w h e n t h e fish were apt to c o m e b e l o w in large batches. ( R e g a r d ing delay in cooling fillets, see Section V I I , A , 3 . )
C. E V I S C E R A T I O N AND R E M O V A L O F G I L L S
According to general practice and supported b y official regulations in some countries, white fish, such as cod, most flatfishes, and t h e larger species o f fatty fish and sharks, are eviscerated on b o a r d i f the fishing vessel is m o r e than a day or so from port. I n m a n y cases it is thought advisable to gut the fish, even if the b o a t is only a few hours out.
T h e r e are two reasons generally given for gutting fish at sea. First, it is said that b e c a u s e of t h e large n u m b e r o f b a c t e r i a in t h e intestines, the partially digested food in the fish would soon b e c o m e sour or putrid.
T h e second ( a n d perhaps more i m p o r t a n t ) reason cited is, as discussed previously, the continuous action of t h e digestive juices of the fish ( s e e further V o l u m e I, C h a p t e r 16, and V o l u m e I I I , C h a p t e r 6 ) .
Herring, mackerel, and other small pelagic fishes are not gutted at sea b e c a u s e of their size and normally l a r g e number. I n case of heavy catches, white fish also c o m e on d e c k in large numbers and it would speed up handling i f one did not h a v e to gut the fish. W i t h t h e great influence of temperature in mind, one would think it quite possible that immediate icing of the round fish would improve t h e quality of t h e fish more than gutting and icing several hours later. E x p e r i m e n t s comparing storage life of gutted and ungutted fish are therefore of considerable interest.
Castell and M a c C a l l u m ( 1 9 5 3 ) found that fillets from ungutted floun
ders that h a d b e e n i c e d immediately after b e i n g caught and h a d not b e e n stored for m o r e than 4 days did not spoil m o r e readily t h a n similar fillets from gutted fish. After 7 or m o r e days in ice, however, t h e fillets from ungutted fish w e r e definitely worse that those from gutted fish. Proctor et al. ( 1 9 5 0 ) , comparing eviscerated and round h a d d o c k kept in i c e , found, contrary to w h a t might b e expected, that after 1 0 - 1 2 days t h e contents of T M A and volatile acids w e r e higher in t h e flesh of the evis
cerated fish than in that of the round fish. T h e y suggested that t h e pres
ent p r a c t i c e b e c h a n g e d , b u t r e c o m m e n d e d bleeding of the fish before
stowing in i c e in order to avoid dark-colored fillets. A repeat of this work with more intensive sampling and organoleptic testing is desirable.
Stansby and L e m o n ( 1 9 4 1 ) , examining a large n u m b e r of whole and eviscerated i c e d mackerel over a period ranging from early summer to late autumn, found that the gutted fish kept from 4 1 to 1 7 7 % longer than the whole fish. T h e greatest improvement was in cases where consider
able red feed was present.
Bystedt ( 1 9 5 3 ) found that evisceration of mackerel did improve the keeping quality of fish stored at 5 ° C . / 4 1 ° F . , b u t that no such improve
m e n t could b e shown for fish stored at 0 ° C . / 3 2 ° F . or 2 ° C . / 3 5 . 6 ° F . As an explanation h e suggested that bacterial spoilage is more easily c h e c k e d than fat oxidation b y lowering the temperature. T h i s oxidation (i.e., rancidity) is particularly noticeable in the belly of the cleaned fish, presumably b e c a u s e of t h e greater access of air to the flesh.
T h e influence of evisceration on the eventual quality of the fish, as well as the extent to w h i c h it is important to avoid contamination of the fish on deck from the intestines removed b y gutting (Ludorff and Kreu
zer, 1 9 5 6 ) , n e e d to b e studied further.
S o m e species of fish, apart from t h e pelagic ones, are almost never eviscerated. This applies for instance to t h e grey sole on the North Ameri
can east coast, the rockfish on t h e North American west coast, and the ocean perch ( r e d fish). T h e spines on the gill-cover of the latter species make normal handling somewhat difficult. All three species are generally used for filleting only.
Results from the tropics indicate that the keeping quality of gutted fish is better than that of round fish ( L a n t z and Gunasekera, 1 9 5 5 a ) . Y e t w e are informed that ungutted fish obtain a better price than gutted fish, because certain portions of the entrails of some species of fish are rel
ished b y the consumers.
T h e existing literature, fish inspection regulations, etc., should b e consulted regarding t h e evisceration and cleaning procedures for various species of fish. M u c h unnecessary d a m a g e can b e inflicted upon the fish b y deficient gutting techniques. I n some countries, the best m e t h o d of obtaining t h e longest keeping quality of c o d a n d similar species is thought to b e cutting the throat immediately after the fish is brought over the rail and then leaving the fish to b l e e d for some minutes before gutting. No doubt this is preferable w h e n the fish is salted in order to obtain fish as white as possible. I n other countries, it is c o m m o n to cut t h e throat and gut t h e fish immediately afterwards; this does not seem to reduce the keeping quality of iced fillets ( B r a m s n a e s , 1 9 5 5 ) .
It is a widespread practice among fishermen to remove the gills from larger fish ( c o d , haddock, salmon, e t c . ) in order to increase t h e keeping
time. E x p e r i m e n t s have shown that fish from w h i c h the gills have b e e n removed generally have a b e t t e r odor and a p p e a r a n c e after several days in ice than fish retaining t h e gills. T h i s difference, however, m a y not b e found in the fillets or in the cooked fish ( C a s t e l l and Greenough, 1 9 5 6 , and Anonymous, 1 9 5 7 a ) .
D . W A S H I N G
M a n y data have b e e n collected on the effect of washing fish after gutting on board. T h e results, however, have not b e e n conclusive. Cas
tell et al. ( 1 9 5 6 ) , experimenting at sea with c o d a n d h a d d o c k i c e d in t h e hold for from 2 to 8 days, found no significant difference b e t w e e n washed and unwashed fish. T h e y also stored fillets from these fish with the same result. T h e y c o n c l u d e d that there is very little to b e gained in keeping quality b y washing fish at sea.
E x p e r i m e n t s in Britain (Anonymous, 1 9 5 5 a ) showed similarly that washing as p r a c t i c e d on ships h a d little effect on t h e subsequent quality.
T h e skin of w a s h e d fish was found to have, if anything, a b i g g e r bacterial load than that of unwashed fish.
Others h a v e found that washed, headed, and gutted h a k e kept 9 - 1 0 days instead o f 7 - 8 days for u n w a s h e d controls (Anonymous, 1 9 5 4 ) . O t h e r workers have suggested the use of washing w a t e r with bactericidal effect, e.g., chlorinated w a t e r ( L u d o r f f and Kreuzer, 1 9 5 6 ; L i n d a and Slavin, 1 9 6 0 ) .
T h e s e a n d other results appear somewhat conflicting. T h e question is p r o b a b l y closely c o n n e c t e d with that o f t h e bacterial load on the fish.
I f one is careful, it is obviously possible to r e m o v e t h e viscera intact soon after capture, i.e., b e f o r e the b a c t e r i a penetrate to t h e belly walls, w h i c h in the live fish are sterile. I n such a case, washing the fish might un
necessarily infect t h e b e l l y walls. Less careful gutting would of course lead to greater infection from t h e viscera. I n such cases effective washing in clean w a t e r m a y help.
O n t h e other hand, there are indications that the infection occurring during storage of fish in i c e is a m u c h m o r e decisive factor for the final keeping quality. R e a y and S h e w a n ( 1 9 6 0 ) report from British trawlers that the b a c t e r i a l load in ice lying in the i c e pounds m a y increase, during the voyage, from 1 02 to 1 03 p e r ml. to 1 06 to 1 07 per ml., t h e increase comprising mainly fish-spoiling types. F u r t h e r work in this field would seem of considerable interest.
T h e problems c o n n e c t e d with washing appear to b e the c o n c e r n mainly of the large fishing boats, w h e r e b i g hauls have to b e handled in a short time. O n small boats, it is m u c h easier to perform a carefully evis
ceration and washing. H e r e it is also possible during washing to c h e c k
the evisceration b y running the fingers through the abdominal cavity, thus removing the remaining parts of liver, spleen, gullets, etc.
E . S T O W I N G I N T H E F I S H R O O M
It should b e clear from the preceding text that fish ought to b e iced or otherwise chilled immediately after being handled on deck. I n spite of this, m a n y fishermen all over the world, day after day, land unchilled fish. This is of course mostly t h e case in coastal fishing with short trips.
Moreover, in m a n y small fishing villages, ice is difficult to procure, and the smallest boats m a y even consider it impossible to find room for ice in the boats.
O n the other hand, t h e coastal fisherman, if h e wishes, can land fish in a perfect condition, an opportunity which must b e the envy of his fellow fisherman on distant water trawlers.
1. Boxes
M a n y consider that the best m e t h o d of keeping fish on board is to pack it with ice in boxes. I t seems difficult experimentally to find any difference worth mentioning in keeping quality determined b y taste or chemical methods b e t w e e n b o x e d fish and bulked fish stowed correctly in ice in the hold ( C a s t e l l et al., 1 9 5 6 ; Anonymous, 1 9 5 8 a ) .
M a n y fishermen who have h a d the opportunity, from years of experi
ence, to compare these two methods of stowing fish, express the belief that boxed fish have a shorter keeping quality than bulk-iced fish. T h e reason for this is presumably that when fish are placed in boxes in the fish room of the boats these boxes are normally well filled with ice, but ice is seldom used around the boxes. T h i s means that if a fish is lying against the side of a box, its temperature is often higher than that of a bulk-iced fish completely e m b e d d e d in ice.
T h e above-mentioned comparison b e t w e e n bulked and b o x e d fish is valid only when the iced fish are stored in the hold to depths of not more than 2 - 4 ft., depending on the fish ( s e e Section I I I , E , 7 ) .
M a n y species of fish, particularly, the pelagic ones such as herring, are easily d a m a g e d b y pressure. W i t h such fish the m a x i m u m retention of quality is undoubtedly achieved w h e n t h e fish are b o x e d at sea with ample ice b o t h at t h e bottom and at the top of the box, as well as around the stack of boxes. T h e s e should b e re-iced on top in port with
out disturbing the fish, and sent straight to inland or export markets.
Finally, there is normally a greater space requirement for fish p a c k e d in boxes on board, compared with stowage without boxes. This is of course often the reason for choosing the latter method.
2. Icing Codes
Advice on correct methods for icing fish can b e found in the literature ( C u t t i n g et al, 1 9 5 3 ; M a c C a l l u m , 1955a; B u t l e r et al, 1 9 5 6 ) . Important general rules are: ( 1 ) to start with a clean fish room; ( 2 ) to p l a c e the ice so that it absorbs h e a t entering t h e hold or the pens before it has a c h a n c e to w a r m up the fish; ( 3 ) to lay gutted fish with the belly cavity facing downwards; ( 4 ) to t a k e c a r e that i c e b e in actual, continuous contact with all fish, and that the latter b e stowed in thin layers; ( 5 ) to place sufficient ice against all sides, including the bottoms of pens and shelves to prevent fish from touching t h e sides at any t i m e during t h e voyage. T h e heads of the fish should preferably point towards the sides of the pen. ( 6 ) T o replenish during the rest of t h e voyage any ice that has melted away on top layers of fish.
W h e n the first fish are stowed at the beginning of a voyage, it is advisable to start in a p e n w h e r e t h e two neighboring pens are filled with ice, and to continue this way.
In some cases round fish, such as cod, hake, and haddock, are only iced around the belly a n d the sides b u t not on the top. T h e purpose in such cases is to retain the bloom of the fish. ( S e e further Section I I I , E , 7 , on "shelving," and Section V I , B , 3 , on packing fish in b o x e s . )
F i s h should b e stowed according to species and size, following t h e main principle that two kinds of fish with different keeping qualities must not b e stowed together. Slime from one species m a y discolor other species. A few rules applicable to North Atlantic fish are: d a b and lemon sole should not b e stowed along with plaice, sole, turbot, and halibut;
round fish such as c o d should not b e stowed along with flatfishes, nor cod and ling along with haddock or pollock ( s a i t h e ) . Catfish, skates, rays, and sharks, w h i c h rapidly form considerable amounts of ammonia, should b e stowed separately.
3. Quantity of Ice
O n e pound of ice during melting absorbs 1 4 4 B . T . U . of h e a t from its surroundings. Expressed in metric units, 1 kg. ( 2 . 2 l b s . ) of ice absorbs 8 0 kcal. T h e specific heat of fish is about 0.9, w h i c h means that 0.9 kcal, is necessary to cool 1 kg. of fish 1 ° C . T h e theoretical weight of ice necessary to cool fish from 1 5 . 5 ° C . / 6 0 ° F . or from 2 5 ° C . / 7 7 ° F . to 0 ° C . / 3 2 ° F . is, therefore, about 1 7 % and 2 8 % respectively of the weight of the fish. Actually m u c h m o r e is used on board, namely from 3 0 to 1 0 0 % or even more, b e c a u s e i c e is used not only to cool the fish down but also to k e e p it cool until it reaches port and, in addition, to chill t h e hold, boxes, surrounding air, etc., during the entire voyage.
L u m l e y et al. ( 1 9 2 9 ) m a d e the following calculation for a trawler with a hold of about 2 0 ft. χ 2 0 ft. χ 9 ft. on a 14-day trip with 1 0 days' fish
ing consisting of 4 0 hauls of y2 ton, a total of 2 0 tons of fish. E x t e r n a l temperature of fish, air, and sea was 1 1 ° C . / 5 2 ° F . and t h e air temperature in the fish room was kept at 8 ° C . / 4 6 ° F . T h e sides and the b u l k h e a d w e r e insulated with 6-inch cork, b u t with no insulation under the d e c k a n d in t h e c o n c r e t e floor. T h e amount of i c e necessary appears in the follow
ing tabulation:
Ice (in tons) required to cool catch from 11°C./52°F.
to 0°C./32°F. 2.25
Ice melted by heat entering through sides, roof, and floor of fish room, plus ice melted by incoming air (opening of hatches, etc.), plus ice melting in
ice bunkers 10.80
13.05
O n a 20-day round trip today, the E u r o p e a n distant w a t e r trawlers with insulated fish holds take about 8 0 - 1 0 0 tons of i c e on board, correspond
ing to about 1 ton o f i c e to 2 tons of fish.
M a c C a l l u m ( 1 9 5 5 a ) gives estimates for fish holds outfitted in different ways in medium-sized Canadian trawlers ( 1 1 5 - 1 3 0 ft.) making an 8-day round trip in summertime. A normal c a t c h in these boats is about 5 5 metric tons of fish.
TABLE III
INFLUENCE OF DELAY IN FILLETING ON THE KEEPING QUALITY OF F I L L E T S ^0
Hours at 15°C./59°F. between Keeping quality of fillets kept slaughtering of fish and cooling at 0°C./32°F., expressed in days
of fillets to 0°C./32°F. before pH increased to 7.5
1 11
4 9 ^
10 ey4
a The plant was using live codling as raw material.
0 From van Deurs and Hoff-j0rgensen (1936).
F e w data are available on t h e p r a c t i c e in small fishing vessels, which are mainly w o o d e n boats. As an example it m i g h t b e m e n t i o n e d that in D a n i s h seine-net fishing for flatfish, cod, and h a d d o c k in the North Sea, it is c o m m o n to use one part o f i c e to one part of fish on a 7-day round trip in summer. U n d e r tropical conditions, t h e necessary quantities of i c e m a y b e as m u c h as 3 - 4 times that o f t h e w e i g h t o f the fish ( B r a x t o n ,
1 9 4 9 ) .
W i t h regard to t h e use o f m o r e or less finely crushed i c e a n d o f t h e various types o f so-called "small i c e , " t h e reader is referred to t h e ex-
perience of local fishermen and fish packers and to makers of ice manu
facturing equipment. T h e literature on this subject is very scant.
T h e general experience regarding size of i c e particles is that the m o r e delicate species of fish, such as herring, mackerel, trout, sardine, and sprat, preserve their appearance best w h e n p a c k e d with finely crushed ice.
During manufacture, i c e is commonly subcooled to about — 1 0 ° C . / 1 5 ° F . and stored at around — 6 ° C . to — 1 0 ° C . ( 1 5 - 2 0 ° F . ) . Crushed ice and "small ices" loaded at the same temperature level will maintain their free-flowing properties for some time. W h e n stored or loaded close to its melting point, the ice tends to fuse to a solid mass.
4. Bilgy Fish or "Stinkers"
F i s h merchants dealing in iced fish from distant water boats some
times c o m e across fish which, although they look and feel q u i t e fresh, nevertheless have a characteristically foul odor. T h e s e are known as bilgy fish or "stinkers" and are unfit for sale. E v e n smoking will not mask the odor, w h i c h m a y also persist during freezing and cold storage. O n the other hand, it is a distinctive feature that the stink of a tainted fillet will slowly pass off if it is left exposed to the air ( C a s t e l l , 1 9 5 4 b ; M a c C a l l u m , 1 9 5 5 b ) . This type of spoilage occurs most often w h e n air is excluded from the surface of i c e d fish, e.g., w h e n fish are left in direct contact with slime-soaked wooden boards. Stinkers c a n b e produced b y fastening fish against pen boards and keeping t h e m i c e d for some time ( B u r g e s s and Spencer, 1 9 5 8 ) .
T h e p e r c e n t a g e of anaerobic bacteria is very high in bilgy fish ( M c L e a n and Castell, 1 9 6 0 ) . M e t h o d s of prevention are, therefore, utmost cleanliness together with sufficient air around t h e fish to secure aerobic conditions. T h e muscle of such fish has a higher hydrogen sulfide con
tent than that of similar fish spoiling in the ice but not in contact with wood. Trimethylamine and volatile acid values are usually, but not con
sistently, high in bilgy fish.
5. Cleanliness in Holds
A thorough cleaning and hosing of the hold and pen boards after each journey is an a c c e p t e d rule (Ludorff and Kreuzer, 1 9 5 6 ) . Cutting et al.
( 1 9 5 3 ) r e c o m m e n d washing with hot, nearly boiling, water, or water treated with a powerful disinfectant. T h e y warn rightly against the use of dock water, w h i c h is generally grossly infected. A m o n g disinfectants they r e c o m m e n d hypochlorites m a d e up with water to a strength of about 3 0 0 parts of available chlorine p e r million ( 0 . 3 p e r t h o u s a n d ) . I n some G e r m a n ports, an ampholytic surface-active agent is used in most trawlers.
L i n d a and Slavin ( 1 9 6 0 ) carried out a practical experiment in install
ing chlorinating equipment on a commercial fishing trawler. S e a water containing 5 0 - 6 0 p.p.m. of free chlorine was used b o t h to wash t h e evis
cerated fish at sea and to cleanse the hold of the vessel at the end of each trip. T h e chlorine seemed to minimize the staining of the fillets resulting from bleeding caused b y forking the fish and to reduce instances of bilgy fish. Moreover, t h e chlorinated sea water removed the slime from the deck of the vessel more effectively than did plain untreated water.
A recent attempt w h i c h failed to prove the value of such cleaning and disinfection should b e mentioned ( C a s t e l l et al., 1 9 5 6 ) . T w o identical wooden trawler pens were used. O n e was left dirty after discharge of the previous cargo of fish, whereas the other pen was thoroughly cleaned and disinfected with a strong hypochlorite solution. Samples of iced fish from corresponding places in the two pens were analyzed for T M A and odor after 7 days' storage. No perceptible differences were found. T h e authors remark that an earlier examination of the fish might have shown a difference in quality b e t w e e n the two lots. This might also have b e e n the case if the fish h a d b e e n stored for 1 0 - 1 4 days in the pens.
It is almost impossible to make a significant reduction in the bacteria in soft, water-soaked wooden boards that are impregnated with fish juices b y merely washing and disinfecting the surface. Counts of bacteria on washed and supposedly sterilized boards have yielded up to 5 0 million bacteria per square centimeter.
6. Contaminated Ice
O n e potential source of contamination that apparently needs still further examination is the ice. It has b e e n shown several times that whereas ice has a bacterial count of only 1 02 to 1 03 at the time it is delivered from the ice plant, this count m a y rise during the voyage to 1 0δ to 1 0f in the ice lying in the ice-pounds ( D r e o s t i , 1 9 4 9 ; Castell et al., 1956; R e a y and Shewan, 1 9 6 0 ) . Regarding bactericidal ices, see V o l u m e I, C h a p t e r 17.
7. Protein and Weight Losses
B y far the greatest cooling capacity is released from the i c e b y its melting. B u t melting water carries with it a considerable percentage of the soluble proteins, salts, and other flavoring and nutritive substances in the fish ( D y e r and Dyer, 1 9 4 7 a ) .
Analyses of the fluid squeezed out of the fish under pressure in a trawler pen showed that about 3 % of the edible protein is lost if a c a t c h loses, on the average, 6 - 7 % of its weight on a voyage (Cutting, 1 9 5 1 ) .
B a r k e r and Idler ( 1 9 5 5 ) storing non-eviscerated salmon in ice found a loss of 2 . 5 % of the total protein in 7 days.
W e i g h t losses of this order are well known to the industry. I n ex
tensive experiments on distant w a t e r trawlers, Cutting found an average of about 2 % loss of weight after 7 days, whereas after 1 7 - 1 8 days in ice, cod from the b o t t o m of a p e n (usually 3 ft. d e e p ) h a d lost 1 0 - 1 3 % in weight, h a d d o c k somewhat more, as c o m p a r e d with a few per c e n t of weight lost b y fish at the top. T h e average was b e t w e e n 8 and 9 % loss of weight. I n control fish stowed in shallow boxes with ice, there was no loss of weight b u t rather a slight gain ( a b o u t 1 % ) . D e p t h of stowage was found mainly to affect the external a p p e a r a n c e of the fish, making 2-week-old fish look 2 - 4 days older than the controls ( R e a y , 1 9 5 1 ) .
Castell et al. ( 1 9 5 6 ) found the same results comparing fish from pens with more shelves t h a n normal with fish from a pen w h e r e the shelves were omitted altogether. H e also noticed that the texture of the fillets from the b o t t o m of the pen without shelves was very soft. C o m p a r i n g the quality of the fish from top to b o t t o m of the pens, w h e t h e r with shelves or without, Castell and co-workers r e c o r d e d that the fish in the lowest section deteriorated more quickly t h a n those above, but the differ
e n c e after about a w e e k in ice was not great.
I n Cutting's experiments, "shelved fish," w h i c h usually means fish laid out regularly, one layer deep, on a b e d of ice, showed losses in weight similar to those in fish from tops of pens. I f the p r a c t i c e of "shelving" is carried out with a whole load, it means about 5 % more fish landed. T h e disadvantages are larger space requirements, m o r e labor, and a some
what shorter keeping quality, since, b e c a u s e shelved fish are not buried in ice, their temperature is a few degrees higher than that of normally iced fish (Anonymous, 1 9 5 6 a ) , the difference obviously depending on the air temperature in the hold.
IV. Fish Hold Outfitting
A. L I N I N G O F T H E H O L D AND P E N B O A R D S
F i g u r e 6 shows the typical construction of a fish hold in a large trawler.
T h e fish rooms in smaller vessels do not, in principle, differ m u c h from this. T h e floor of the hold, in w h i c h drain channels a r e cut running fore and aft, is concrete. T h e channels empty the melting ( b i l g e ) w a t e r into the well.
1. Wood
T h e most c o m m o n l y used material for the side lining, intermediate wing bulkheads, and loose pen boards is w o o d c o a t e d with shellac, var
nish, or special types of white fish-room enamels or lacquers. Quality of
material, workmanship, and painting, and subsequent cleaning and maintenance are governing factors in the successful use of wood, b e c a u s e this material requires constant vigilance in order to prevent its b e c o m i n g damaged, water-soaked, and consequently contaminated with slime and bacteria.
WELL
FIG. 6. The inside of a large trawler fish room. The concrete floor has two channels that deposit the water from the melting ice into a well connected with a pump. Galvanized steel pen-board stanchions (studs) make possible the division of the fish room into pens. Such a pen is shown, where the pen boards are made of wood (Fisheries Technological Laboratory, Copenhagen).
M a c C a l l u m ( 1 9 5 5 a ) stowed iced fish in the laboratory and on board a ship against various materials used for lining. H e examined worn wooden boards, freshly planed and painted or varnished boards, and transparent plastic and aluminum alloy sheets. H e found that strong bilgy odors developed quickly in the fish against the worn boards, while almost all fish in contact with the other materials ( a l u m i n u m sheet b e i n g the b e s t ) , w e r e free from bilgy and sour odors. No benefit was derived from brushing and washing the worn boards in w a r m water. M a c C a l l u m draws attention to the well-known fact that it is very difficult to keep wooden boards well painted or varnished and he therefore suggests that metal lining b e m o r e widely used.
2. Metal
O n the other hand, it is true that aluminum or other light metal alloys h a v e many advantages and in recent years these have b e e n installed in
