Effects of dietary vitamin A on growth, hematology, digestion and lipometabolism of on-growing gibel carp (Carassius auratus gibelio var. CAS III)

•Dietary vitamin A requirement of on-growing fish was lower than juvenile fish in gibel carp.•The influence of dietary vitamin A on GH/IGF system and digestibility of fish was evaluated in the present study.•Vitamin A deficiency decreased lipid utilization and appropriate dietary vitamin A enhanced antioxidant status of fish.•High dietary vitamin A decreased the intestinal absorption ability and induced the lipid accumulation of liver.

A 106-day growth trial was executed in a flow-through system to investigate the effects of dietary vitamin A on growth, hematological indices, digestive functions, body composition and lipid metabolism of on-growing gibel carp (69.39 ± 0.08 g). Fish were randomly assigned to seven groups and fed with different diets containing 273, 1278, 1962, 3155, 4105, 4931 and 5751 IU vitamin A kg− 1, respectively. Specific growth rate (SGR) and feed efficiency (FE) of gibel carp were lower at 273 and 5751 IU kg− 1 vitamin A levels (P < 0.05). Hemoglobin content in blood, and the levels of plasma growth hormone (GH) and insulin-like growth factor I (IGF-1) were not significantly influenced by dietary vitamin A (P > 0.05). Although the apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid and energy were not influenced significantly (P > 0.05), high dietary vitamin A (5751 IU kg− 1) decreased the activity of intestinal Na+–K+ ATPase (P < 0.05). The plasma total antioxidative capacity (T-AOC) was improved at the levels of 1962 and 3155 IU vitamin A kg− 1 (P < 0.05). Vitamin A deficiency increased the activities of plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) (P < 0.05), and decreased the contents of whole body and liver crude lipid and the plasma cholesterol content (P < 0.05). Plasma cholesterol and vitamin A contents were significantly increased (P < 0.05) and then leveled off with the increasing of dietary vitamin A level. Broken-line regression between dietary vitamin A level and plasma cholesterol content or plasma vitamin A content indicated that the dietary vitamin A requirement of on-growing gibel carp was to be approximately 1716 IU kg− 1 and 2698 IU kg− 1, respectively. 2698 IU vitamin A kg− 1 diet is recommended for on-growing gibel carp in the present study.