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.