Tuna long liner  is a ship specialized in tuna fishing, which is composed of trunk lines ranging from several kilometers to hundreds of thousands of meters, branch lines, hooks and baits. It is an oceanic fishing boat. It usually enters the port once a year, and the ship is equipped with perfect fishing equipment and quick freezing and refrigeration equipment. The capacity of frozen catch is strong. The catch is usually separated from fishing on the deck to entering the market for more than half a year.

The price of tuna is closely related to its freshness. The higher the freshness, the higher the price. Therefore, there are higher requirements for the preservation of fish catches. The temperature of the ultra-low temperature refrigerated fishing tank can reach -55℃, and the temperature of the ultra-low temperature quick-freezing tank can reach -60℃.