92 DESCRIPTION OF IMPORTANT FISHERIES AND THEIR PRODUCTS 



fishing commences. Tuna is allowed to accumulate on deck during a bait 

 boat operation until a school is lost or the ''rail is full." Then it is thrown, 

 slid down troughs, or flumed into the wells. When seining, fish is brailed 

 directly into hoppers from which it runs by troughs into wells. Fish 

 temperatures may be 65 to 90°F, causing a temporary warming of the 

 circulating sea water, but this then usually cools to 30 to 32°F in 24 hours 

 under refrigeration. 



Tuna is buoyant in sea water, and when the well is apparently filled, 

 it can still accept another 20 to 25 per cent of fish. Water from the cir- 

 culating system is therefore discharged overboard or to another well, 

 causing the level of sea water and fish to sink and allowing more fish to 

 be packed under the well overhead. When this operation is completed, a 

 wooden grating is lodged at the bottom of the coaming to hold down the 

 fish when the denser freezing brine is circulated. 



While it is economically important to stow a maximum of fish in a well, 

 pumping too low or forcing too much fish into the top puts excess weight 

 on the still soft fish below which distorts and flattens it. Pressing it 

 together reduces the exposed surfaces through which heat may be 

 extracted and, at the same time, closes up the structure of the load, 

 greatly impeding the flow of brine. This is especially true with the softer 

 and smaller skipjack. The result is to slow the cooling, which may then 

 permit bacterial spoilage and heavy salt penetration. At the thawing 

 stage, the slower passage of brine through over-packed wells can cause 

 complete icing with considerable loss and delay. 



When the well has cooled to 30 to 35°F, it is ''brined." Cold brine may 

 be transferred from another well, or the salt content of the water in the 

 well may be increased as required by pouring salt into the coaming 

 where it is dissolved by circulating liquid. Enough salt is generally added 

 to give a brine freezing about 5°F below the temperature at which it is 

 intended to hold the fish. Thus a 13 per cent brine freezing at 15.7°F 

 might be used to cool to 20°F, at which temperature approximately 90 

 per cent of the water in the tuna would be frozen. 



It is important to lower the temperature of the water before the salt 

 is added. Lang and Farber^^ demonstrated that salt penetrates much 

 more rapidly into the fish muscle at higher temperatures, and an excessive 

 salt level in the fish results from prolonged contact with brine above 

 freezing. 



When the brine is first circulated, the fish temperature drops slowly 

 while most of the water in the tuna is being frozen, then more rapidly. 

 After about three days, the well is "dried up" by pumping the brine 

 overboard or to another well. This not only reduces salt penetration, 

 which would result from continued contact of brine with the fish, but 



