Dietary choline requirement in slight methionine-deficient diet for juvenile gibel carp (Carassius auratus gibelio)

A 10-week feeding trial was conducted in a flow-through system to determine dietary choline requirement for juvenile gibel carp (Carassius auratus gibelio) (5.5 ± 0.1 g). Purified basal diet was formulated using vitamin-free casein as protein source. Choline chloride was supplemented to the basal diet to formulate seven diets containing 76.1, 163, 356, 969, 1457, 2024 and 4400 mg kg−1 choline. Dietary methionine was 0.58%, less than the requirement (0.69%). The results indicated that specific growth rate (SGR) was higher in the fish fed 2024 mg kg−1 diet than the control group. Feeding rate and feed efficiency were not significantly affected. Protein productive value increased as dietary choline increased from 76.1 to 2024 mg kg−1 diet and was lower in the fish fed the diet containing 4400 mg choline kg−1 diet. Serum high-density lipoprotein cholesterol (HDL-C) and total cholesterol significantly increased with increasing dietary choline up to 1457 mg kg−1, and no differences were found with further increase. Fish carcass fat contents decreased significantly with increased dietary choline. Hepatic lipid contents increased with dietary choline up to 1457 mg kg−1 and then decreased. Quadric regression of SGR and plasma HDL-C indicted dietary choline requirement was 2500 and 2667 mg kg−1 diet, respectively.