Tuna Fishing and Ice-Fresh Processing Techniques

Tuna is a highly migratory marine fish with delicious meat and high nutritional value, deeply loved by consumers, and has therefore become one of the key fishing targets for fishing nations.

I. Handling on Deck

1. Avoid bruising the fish: After the fish is on deck, it must not be allowed to thrash around, to prevent internal bruising. After bruising, it causes damage to 5 times the area of muscle, especially in the belly. The method is: place it on a carpet, press both hands on the fish's eyes, or strike the fish's head with a hammer, but be careful not to break it open, then bleed it

2. Tail cutting: Usually a sharp knife is used to cut between the 3rd and 6th vertebrae from the tail. For larger fish, to prevent the tail from being too thin after cutting, cut between the 4th and 5th vertebrae from the tail.

3. Cutting the blood vessels: Tuna usually has two blood vessels, an artery and a vein, behind the pectoral fin. Cut where they separate. The cut should be 5 cm deep and 4 cm long. The depth must be appropriate; if the cut goes in too deep, blood will seep into the inner meat and cause waste. Even if the fish has already died in the water, the above operations must still be carried out.

4. Cutting the cephalic artery in front of the heart: Cut the cephalic artery in front of the heart, rinse the fish body with seawater to prevent the fish's body temperature from rising, then carry out the bleeding operation. Cut a hole in the inner membrane of the gills to drain blood, insert a hose and flush seawater in from there until there is basically no blood left. Whether the blood is fully drained is judged by the tail.

5. Inserting the pin behind the head: The pin is inserted after the bleeding operation is completed. This operation aims to destroy the cartilage of the fish's brain, leaving the fish in a dead state. The pin is inserted at the inner point of the head, or at the depression, or at the top of the head above the fish's eye.

6. Removing the viscera and gills: Use a sharp knife to cut open the belly from the anus to the pectoral fin, take out the viscera, and rinse clean with seawater. During the operation, note that the membrane attached to the inner wall of the abdominal cavity must also be removed, and the abdominal cavity rinsed with seawater. To cut the gills, slit the gill bone membrane along the edge of the gills and remove part of the gills. When removing the gills, the cut at the rear of the gills should be as large as possible; it is best to push the knife flat along the inner side of the gills until it touches bone, then cut straight down through the gills from the upper part, so that the product looks good. After removing the gills, use a small spoon to scrape off the stray meat attached to the bone inside the gills, but do not tear the meat inside the gills.

7. Washing: When brushing and washing the fish body, you must brush from the tail toward the head, then give it a seawater bath, and then proceed separately from the preparation room to the freezing room to apply an ice glaze, keeping it cold, so that the commercial fish meets the requirements for high quality and high price.

II. Ice-Fresh Process

1. Treatment of the bilge and bulkheads: The bilge and bulkheads should be lined with 30 cm of ice. Place the fish 30 cm away from the bulkheads and fill the gaps with ice.

2. Stuff ice into the belly cavity through the fish's mouth, filling it firmly and completely.

3. Placement: Lay the fish flat, with 30 cm between fish, filling the gaps with ice. Each layer of fish must also maintain a 30 cm layer of ice. Between layers, the fish should be placed in a staggered pattern, forming a triangle, with heads and tails reversed. After arranging, seal with ice and cover with an ice quilt, and the ice-fish process is complete.

4. Breaking the ice and covering with ice twice: Generally, on the day before icing the fish the next day, the ice covering the fish from the previous day should be broken up again, a layer of ice spread over it, and then the fish iced again.

5. The temperature of the ice-fresh fish hold should be controlled between 0~2°C, and must not exceed 5°C at the highest.

6. The shelf life of ice-fresh fish is 12 days; 14 days is the limit. Beyond 14 days, it will gradually deteriorate.