The research programme on disease of marine fish was discussed with Dr. Ilan Paperna, Hebrew University, at the Marine Biology Laboratory (see Section 7). Particular emphasis was placed on problems related to imbalanced nutrition and byproducts of diets adversely affecting fish, notably Sparus auratus. Two such problems noted and diagnosed were Visceral Granuloma (VG), affecting spleen, kidneys and liver, and fatty liver (Lipodal Liver). Current and projected experiments are designed to evaluate the effect of the fish meal component of the diet on the VG disease. Since a rancidity factor is suspected as the prime causal agent, experimental dietary design will involve formulations of a) de-fatted fish meal, b) extracted fats added to neutral proteins, and c) non-fish protein. Other fish meals also will be tested. Plans are to follow up on the “rancid factor”, to evaluate relationship to vitamin deficiencies and specific vitamins, as well as mode of action of the VG syndrome. Positive correlation of 70 with diet characteristics indicates the need to dovetail the design of nutritional experiments with evaluation of effects on VG and other pathological conditions.
The fatty necrosis of the liver may be due in part, or entirely, to the high levels of carbohydrates and saturated fats in the current grow-out diets. Modified diets are being designed to diagnose the problem. Since the liver necrosis can be detected within the first 2 ½ months of growth, dietary work will include an ancillary diagnostic programme for detection of fat vacuoles in the liver. Appropriate dietary modifications are planned to establish the causal factor and mode of action of the fat accumulation.
