Lordotic Deformation and Abnormal Development of Swim Bladders in Some Hatchery‐Bred Marine Physoclistous Fish in Japan

At many hatcheries in Japan, a high incidence of lordosis is being reported among marine physoclistous juveniles of red sea bream, Japanese sea bass, and amberjack. Extensive studies being conducted since 1975 to tackle this problem have led to the following conclusions, and effective countermeasures are being proposed. During early larval development in the temporary physostomous stage, fish must be able to gulp air at the water surface for normal development of the swim bladder. The juveniles that fail to gulp air swim upward in an oblique position because of insufficient buoyancy, causing the backbone to curve in a V‐shape. The managerial solutions proposed are: 1) reduce the strong water current caused by vigorous aeration; 2) provide nutrient‐enriched rotifers to produce healthy swimming larvae; and 3) prevent any oily film formation on the water surface.