Tuna is divided into six types: yellowfin tuna, bigeye tuna, albacore tuna, skipjack tuna, bluefin tuna, and masu tuna.

1, yellowfin tuna body is fusiform. Slightly laterally compressed, the tail is longer and thinner, the adult second dorsal and anal fins are extended, the ventral fins are pectoral, the caudal fin is crescent-shaped, the caudal peduncle is well developed, and there are three bulges on each side. The jaws are denticulate, tapered and arranged in a row. Body covered with fine scales, the scales on the thorax are larger, forming a pectoral armor. The lateral line is distinct. The highest part of the body is located in the middle of the base of the first dorsal fin.

2, bigeye tuna: body length 2m, weight 150 kg or more, body shape similar to bluefin tuna, pectoral fins are larger, eyes are larger. The body is thick spindle eye shape, very thick, so it is also known as "fat belly tuna", the middle of the body in front of the sub-cylindrical, cross-section nearly round, tail is very short; high body, big eyes, big head.

3, albacore tuna: head longer, body length nearly 4 times the length of the head; pectoral fins are very long, sickle-shaped, length is greater than the head length, the end of the second dorsal fin to reach the vertical line on the starting point; tail fins on both sides of the three elevated crest. Dorsum dark, abdomen pale, body color uniform. The small fins are lemon yellow.

4. Skipjack tuna: thick body, rounded in cross section. The second dorsal and anal fins have 7~8 small fins behind each. The back of the body is blue-purple, the abdomen is silver-white, and there are 4-6 obvious black longitudinal bands on the ventral side of the body, which is why it is called "six stripes".

5, compared with the yellowfin tuna and bigeye tuna, bluefin tuna has a large age of sexual maturity, spawning grounds are concentrated and shorter spawning period and so on.

6, Masu tuna is carnivorous, with a wide range of diet, mainly skipjack tuna and mackerel small fish, mysid shrimp and squid, and is an impatient predator.

Expanded Information:

Preservation

1, chilled method

This is a common and simple and easy to implement preservation method, in addition to crushed ice, but also in the ice when adding 3 ~ 7% NaCl, appropriate amount of sorbitol and composite food phosphates, the fish will be cleaned and cut into 3cm ~ 5cm thick fish fillets, put into a plastic film bag, and then put into a plastic frame at 2 ° C ~ 4 ° C cold storage in the form of layer of fish layer of ice, the small tuna can not be sliced, directly covering the Crushed ice.

2, micro-frozen freshness

3cm ~ 5cm thick tuna fillets placed in -1 ° C ~ 3 ° C conditions for micro-frozen freshness, generally can be kept fresh for 8 days ~ 10 days, the color and flavor of the meat remains unchanged, can be used as sashimi.

3, gas-conditioning preservation

Fresh tuna cut into polyethylene bags, and then filled with a certain percentage of gas mixture (N215%~20% O215%~21% CO260%) sealed packaging, can effectively prevent muscle color changes, such as the combination of 0 ° C low-temperature storage, freshness period of up to 20 days -25 days; micro-frozen storage, freshness period of up to 30 days. If combined with 0°C low-temperature storage, the freshness period can reach 20-25 days; microfrozen storage, the freshness period can reach 30-40 days.

Baidu Encyclopedia - Tuna