Evaluation of Growth and Histology of Liver and Intestine in Juvenile Carp (Cyprinus carpio, L.) Fed Extruded Diets with or without Fish Meal

Growth and histology of intestine and liver of carp fed diets with or devoid of fish meal (FM) was studied. Carp were fed four experimental diets formulated to contain 38% protein for 90 days. FM was incorporated at 30% in feed A, 15% in feed B and C, and was completely replaced with a mixture of plant proteins in feed D. Feed C and D were supplemented with methionine and lysine. The results showed that carp fed feed D had the lowest weight gain, length and height compared to the other three diets, whereas no differences were observed between A, B and C for the measured morphometric parameters. Inclusion of methionine and lysine tended to improve SGR of carp fed feed C compared to those fed feed B, but growth rate was lower than carp fed feed A. FCR differed for nearly 90% between the FM rich and solely plant protein diet. No major pathological changes were recorded. At the end of the study shortening of intestinal folds' length was found for all groups, except for fish fed feed D. The height of enterocytes was significantly lower for carp fed diet D compared to other diets. According to the results obtained the best diet is feed A, but feed C with 15% FM and added methionine and lysine represents an acceptable replacement due to its lower price and effect on growth that are the most similar to feed A.