In Japanese fish markets and seafood restaurants, fish such as sea bream, flounder, and fugu are sometimes kept alive in tanks. These fish may be traded as katsugyo—live fish—and transported alive to restaurants.
Why go to the trouble of keeping them alive?
One major reason is that markets, restaurants, and chefs can choose when the fish is killed and prepared.
After a fish dies, the condition of its flesh gradually changes. If it is transported alive, it can be killed at the desired time, bled properly, and, depending on the fish, processed using shinkeijime, a technique that destroys the spinal cord and nerves. These methods make it easier to control freshness and the condition of the flesh.
Fish that has only recently been killed can have a distinctive firmness and bite. When that texture is important, as it can be with some sashimi, keeping the fish alive until shortly before preparation has a clear purpose.
However, a fish is not automatically at its most delicious simply because it is still alive.
The flesh continues to change after death, and flavor can deepen as time passes. Depending on the species and the dish, waiting for a while may produce a better result than serving the fish immediately. A chef may choose when to kill and serve the fish depending on whether the goal is firmer texture or more developed flavor.
A tank also gives customers a very visible sense of freshness. If a fish was swimming moments before being prepared, it is easy to think, “That must be extremely fresh.”
At the same time, not everyone reacts in the same way. Seeing the fish alive can make its freshness obvious, but it can also make some people think, “I feel a little sorry for it.” A person may appreciate the freshness without necessarily enjoying seeing the animal alive just before it becomes food.
So katsugyo are not kept alive simply for display. By delivering fish alive to markets and restaurants, sellers and chefs have more control over when and how the fish is killed, and over the condition in which it is ultimately prepared.
