On average skipjack tuna is at 30 degree when it is caught from the ocean. Fish processing companies have a standard to keep tuna fresh with minimum 12 degree. Fishermen catch the fish while standing on the rear of the vessel and throw it on to the open decks of the vessel. The fish us usually gathered on the deck where some crew members will throw water on top of the catch to keep it fresh.
Once the fishermen are done with catching the fish for the day they thoroughly clean the deck and fish shortage area, dry up the blood and water from the area, so as to ensure fish can be kept fresh for longer. Modern vessels are designed in a way to allow fish to be kept on the area while blood and water is dried using a pump. The catch is also cleaned thoroughly with water.
Once the fish and storage area is cleaned thoroughly, melted ice is put in the area where the fish will be stored. Once the fish is submerged with the ice water, ice chips are poured on top of it. The most important part of this process is using a pump system to recycle the cold water to keep the temperature at the right level to ensure fish stays fresh. This process melts the ice on top and creates the right level of ice water to keep the fish at the exact required temperature set by processing companies.
If its 3-4 tons of fish, it would require 200 kilos of ice to recycle water within the storage. This helps to reduce the fish temperature quickly ensuring it doesn’t dry and it stays fresh. Fishermen have to use 1 ton of ice to deliver 3 tons fish to processing companies at the standard and quality required for export. This is the normal process followed by fishing vessels to keep fish fresh.
In some local vessels, fish has to be taken out of the deck storage, cleaned and ice poured on top of it. This is done in layers. But this does make it more costly as it would require a lot of ice. This particular process would require 1 ice ton for 1 ton of fish.
This process is made easier for vessels with its own ice making mechanisms or systems (RSW). If they have their own system to make ice, fishermen will clean and hand over the fish to crew members handling the ice making mechanism who will set temperature and keep the fish fresh.