Most tuna fish fishing boats make trips lasting for several months and for this reason, the fish are usually frozen aboard the boat.
The freezing process depends on the type of tuna. For bluefin tuna as an example, fisherman first cut the tail and gills, then gut bled and freeze it t -65 C for 35horus before placing them in to the fish hold at -60 C.
Normally in freezing, the whole fish are cooled in large well with refrigerated sweater circulated through it at 28 F (-2.2 C). Once the fish are cook led, the refrigerated seawater is pumped out of the well, and it is replaced with refrigerated bone at 10 F (-12.2 C) or lower.
When the fish are frozen, the brine is pump out of the well, and the fish are kept frozen in the dry well by circulating mechanically refrigerated air.
In one system brine is sprayed on refrigerated pipe coils located in the hold of the vessels until a coating of ice one foot thick or more is frozen. The compartment is then filled with fish and is flooded with brine. Accumulated ice provides refrigeration capacity needed to chill the brine and freeze the fish.
They remain there until the boat arrives at port.
Frozen tuna aboard the boat
