Deformity of the Lower Lobe of the Caudal Fin in Artificially Produced Ayu, Plecoglossus altivelis

Abstract

A deformity consisting of abrupt or steady lateral curvature of the lower lobe of the caudal fin was recognized in artificially produced Ayu, Plecoglossus altivelis, fly. The deformity was related to the current in the rearing tank: a counterclockwise current induced curvature to the left in 6.5 to 23.3% of the fish, whereas a clockwise current induced curvature to the right in 23.3 to 34.5 % of the fish. The deformity rates could be reduced by periodically inverting the current direction and feeding fish with rotifers, Brachionus plicatilis.