Physical damage may occur at almost 

 any step in the handling of fish. Aboard 

 the fishing vessel the most likely areas 

 are during the initial handling, during 

 the chilling and freezing processes and 

 while unloading. 



Further change in the quality of tuna 

 may be due to bacterial and autolytic 

 spoilage. Bacteria are always present and 

 as soon as an organism dies, they multiply 

 and start their work of destruction. The 

 same is true for autolytic or enzyme 

 spoilage. As soon as the organism dies, 

 self-digestion or autolytic spoilage starts. 

 Aboard the fishing vessel the most likely 

 times for spoilage to occur are during the 

 initial handling, during the chilling 

 process, and during the thawing and unload- 

 ing. 



A sidelight on bacterial spoilage is 

 of interest. Canadian research workers 

 have done considerable work on the spoilage 

 of fish, and have evolved a heat-unit 

 concept of spoilage. They conclude that 

 the rate of bacterial spoilage at 37 °F. is 

 double the rate at 32°F. or, in general, 

 that the rate of spoilage doubles for every 

 5° rise in temperature above 32°F. 



The third factor, oxidative deteriora- 

 tion, may affect the quality of the tuna 

 during the frozen dry storage period. 

 During this period, oxygen reacts with 

 certain chemicals in the fish flesh, the 

 most noticeable reaction being the develop- 

 ment of rancid odors and flavors in the 

 fatty flesh. 



The last important factor is salt 

 penetration, which can affect the quality 

 of tuna at any time during chilling, 

 freezing, and thawing. Changes in quality 

 due to salt penetration can be compounded 

 during these periods, due to variations in 

 these processes. 



Not only the bait-boats but also the 

 purse seiners and trollers have some dif- 

 ficulty in maintaining the quality of their 

 fish. An important problem occurs in seine 

 fish while they are in the net. As the net 

 is being brought in, the area in which the 

 fish can swim about is restricted and 

 physical damage may be inflicted by one 

 fish upon another in his death struggle. 

 By the time the net is in a condition to 

 be brailed, most of the tuna have died 



from being confined. Since the water tem- 

 perature is relatively high and because it 

 takes considerable time to brail a net, 

 some autolytic or self-digestion deteriora- 

 tion may take place. Recent improvements 

 in fishing gear have cut down the time 

 necessary to purse the seine and to load 

 the fish into the hold of the vessel. This 

 saving in time will undoubtedly have good 

 effect on the quality of seine-caught tuna. 

 During 1957, another innovation, the brine 

 spray system of refrigeration, was adopted 

 by a member of the San Pedro seine-boat 

 fleet. Since that time several other boats 

 have installed similar systems, and the 

 percentage of reject fish is reported to 

 be low at the present time. 



The tuna trollers are primarily short- 

 range fishing vessels. If the fishing is 

 good, there is the possibility that the 

 tuna will be on deck too long at high tem- 

 peratures. In such cases, the fish lose 

 quality due to autolytic and bacterial 

 decomposition. These boats use ice to 

 refrigerate their fish. Because of this, 

 there is a possibility that some physical 

 damage can occur through the use of too 

 large and sharp pieces of ice. Also troll 

 caught tuna held in ice, can suffer from 

 bacterial and autolytic spoilage and from 

 oxidative deterioration, if the boat re- 

 mains out too long. 



In collaboration with the California 

 Fish Canners Association, a man with ex- 

 perience, both as a fisherman and as a 

 research worker, was detailed to a tuna 

 clipper for two trips to study some of the 

 variables in the handling and freezing of 

 tuna at sea. Aboard the vessel, samples 

 of tuna were tagged and records were kept 

 of the temperature and handling conditions. 

 Logs were maintained for each brine well 

 in order to indicate the variables en- 

 countered commercially in handling, loading 

 chilling, and freezing the fish. In addi- 

 tion, samples of tuna were taken at various 

 intervals and were frozen in still air in 

 the meat locker for later studies of oxida- 

 tion, salt content of the fresh flesh, and 

 on salt absorption during storage in re- 

 frigerated brine ashore. 



Several observations made aboard the 

 vessel during the two trips are of interest 

 in relation to the time and temperature 

 delays which may occur in the handling, 

 chilling and freezing of tuna. The following 



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