PURPOSE: To make the growth and develonment of fishes, etc. better, by adding an alkali alginate and an organic acid stronger than acetic acid to a blend of one or more selected from the group consisting of vegetable protein, fish meal, activated sludge, ground fresh fish, etc.

CONSTITUTION: An alkali alginate is added to a blend of one or more selected from the group consisting of vegetable protein, fish metal, activated sludge, ground fresh fish, etc. main ingredients of a feed, and an organic acid stronger than acetic acid in an amount to adjust pH to about 4 is added to the blend, to prepare a feed. For example, 10kg sardine is minced, 50g alkali alginate powder is added to it, stirred fully and dissolved. A solution of 20g citric acid in 1 little water is added to the sardine product, which is allowed to stand. The product is jelified in about 5min, to form a solid feed in pH4.2. Citric acid, malic acid, tartaric acid may be cited as the organic acid stronger than acetic acid.