278 PRESERVATION METHODS 



It is usually desirable, where possible, that all fish be dressed, i.e., 

 gills and viscera removed, immediately after catching. The gut cavity 

 should be washed with clean sea water before icing. Recent tests aboard 

 an Atlantic trawler^ showed that use of 50 ppm chlorine in the sea water 

 was more effective than plain sea water in rinsing the blood and slime 

 from the fish. In some fisheries, e.g., the Pacific trawl fishery, dressing is 

 deemed impractical for the value and size of the fish. Experience in the 

 distant water trawl fishery of Great Britain has demonstrated the im- 

 portance of gutting and washing the fish^ 



Chilling Procedures. Lowering the temperature of the fish by a prompt 

 and efficient chilling procedure is fundamental for preservation of fish 

 freshness. Proper use of crushed fresh water ice is the oldest and simplest 

 method. 



Use of Ice: The most significant rule in use of ice or any chilling pro- 

 cedure is that eventual spoilage is only retarded, not stopped^ 



Ice, when properly used in adequate amounts, aids in preservation in 

 two ways: (1) the temperature of the fish is lowered to approximately 

 32 to 36°F, which slows the bacterial and enzymatic changes and (2) the 

 melting of the ice bathes the fish in clean cold water and, with proper 

 stowage, washes away considerable slime, blood, and bacteria. 



Every pound of ice, on melting, absorbs 144 BTU of heat from its sur- 

 roundings. This absorption of heat is sufficient to lower the temperature 

 of 19 pounds of fish 10 degrees Fahrenheit (assuming that the fish has a 

 specific heat of 0.760 and that no external heat was absorbed in the 

 process). In actual practice, the heat transfer from the boat hold and air 

 equals or exceeds the heat transfer from the fish. 



To ice the fish correctly in the boat hold, three things should be accom- 

 plished : first, the fish should be placed with sufficient ice around them to 

 cool them promptly and to maintain their temperature as close to the 

 melting point of the ice (32°F) as is practical for the duration of the trip; 

 second, the ice and fish should be arranged to allow accumulated water, 

 blood, and slime to drain through the mass into the bilge; and third, the 

 fish should not be subjected to great pressure from the weight of fish and 

 ice placed above. Otherwise, the physical damage as well as the shrinkage 

 or loss of weight by the fish will be excessive. 



Every fisherman soon learns how much ice to ''take on" to carry him 

 through the trip. The expected duration of the trip, the temperature of 

 air and sea water, the insulating value of the sides and deck head of the 

 vessel, and the expected quantity of fish to be obtained are all factors 

 to be considered in estimating the amount of ice to be loaded. Ice is cheap 

 compared to the other expenses of a fishing operation; hence, no fisher- 

 man should cut short his estimated need. The exact ratio of weight of ice 

 to weight of fish to be carried varies commonly from 1 :4 to 1 : 1. In north- 



