Fatty acid composition, growth and morphological deformities in juvenile cyprinid, Scardinius erythrophthalmus fed formulated diet supplemented with natural food

Response of a freshwater cyprinid fish Scardinius erythrophthalmus juveniles (initial age 195 days, initial weight 0.82 ± 0.06 g) to supplementation of a formulated commercial dry diet with natural food was examined. A 90-day experiment at 25 °C consisted of two periods. During 60 days three feeding groups were studied: the group F received the dry diet Futura exclusively, the group FC was fed Futura supplemented with frozen larvae of Chironomidae, and the group C received exclusively chironomids. This was followed by a 30 days “recovery period” during which all fish received larval chironomids, only. No mortality occurred during the experiment. The poorest growth was found in the F group, in the supplemented group FC growth was intermediary, and the best growth took place in the C group. The highest condition coefficient was in the group F, the lowest one in the group C. In the group F incidence of spinal curvatures was the highest (77.8% on day 60), in the group FC it was intermediary (42.2%) while no body deformities were found in the group C. After a month exclusively on chironomids (day 90) percentage of deformed fish declined to 66.3 and 31.3, respectively, for the groups F and FC. The proportions of fatty acids in Futura were typical of a formulated diet based on n−3 rich oils: a high concentration of n−3 PUFA (26.9% of total fatty acids, predominantly docosahexaenoic acid DHA, C22:6n−3), and a low concentration of n−6 PUFA (4.9%). In contrast, chironomids contained only 5.9% n−3 PUFA, and a high concentration of n−6 PUFA (28.8%, mainly linoleic acid LA, C18:2n−6 and arachidonic acid AA, C20:4n−6), which compares well with natural food of freshwater fish. Fatty acid composition of fish whole body lipids reflected the fatty acid profiles of the respective diets, while chironomid supplementation to Futura resulted in intermediary values. Diet-induced change in the fatty acid profiles seems to be a relatively slow process. Supplementation of formulated dry diets deficient in n−6 fatty acids with natural invertebrate food could be regarded as a technique to mitigate body deformities in freshwater fish juveniles. We suggest that the diets manufactured for freshwater juveniles should resemble their natural invertebrate prey.