Simplification of changing rearing tanks in the rearing procedure for Japanese eel Anguilla japonica larvae

In the current rearing procedure for Japanese eel Anguilla japonica larvae, it is essential that rearing tanks are changed by transferring larvae into a clean tank by siphoning every day or once every few days. This process is accompanied by a risk of losing larvae, and this risk is reduced by conducting the operation by hand. Thus, it is difficult to operate a number of rearing tanks and to rear larvae on a large scale under the current rearing procedure. To solve this problem, we first reconfirmed that a change of rearing tanks improved larval survival. Then, we tested two schemes for simplification of the processes of changing rearing tanks. One is that the rearing water is dropped from elevated tanks into clean tanks by siphoning, and then decanted into the clean tanks. Another is that changing tanks is omitted and the wall and bottom of tanks were wiped. We demonstrated that larvae could be safely reared to glass eels by each method. These results suggested that transferring larvae between tanks could be simplified and could be omitted by keeping the wall and bottom of rearing tanks clean.