Effects of dietary vitamin C on growth, gonad development and antioxidant ability of on-growing gibel carp (Carassius auratus gibelio var. CAS III)

An 88-day experiment was conducted in a flowing system to evaluate the effects of dietary vitamin C on growth, body composition, antioxidant and gonad development of on-growing gibel carp. Triplicate tanks of gibel carp (77.2 +/- 0.1g) were randomly fed with one of seven experimental diets containing l-ascorbic acid of 0, 101.1, 188.5, 313.1, 444.1, 582.1 and 747.0mg/kg, respectively. The results showed that specific growth rate (SGR) and feed efficiency (FE) of fish were not affected by dietary l-ascorbic acid. Dietary l-ascorbic acid of 444.1mg/kg diet led to low levels (p<.05) of gonadosomatic index (GSI) and hypothalamic gonadotropin-releasing hormone (GnRH) in on-growing fish, as well as the early ovarian stages (Developing stages) compared with fish (Maturing stages) from the other groups. Dietary l-ascorbic acid supplementation increased (p<.05) the dorsal muscle collagen content, but did not affect the protein or lipid content of dorsal muscle in gibel carp. Plasma total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity increased (p<.05) and then remained unchanged with the increase in dietary l-ascorbic acid levels. Dietary l-ascorbic acid of 101.1mg/kg diet improved (p<.05) plasma lysozyme activity of the fish. Broken-line regression indicated that dietary l-ascorbic acid requirement of 77g gibel carp was 223.3 or 225.0mg/kg diet based on plasma T-AOC or SOD activity, which was a little higher than that based on plasma l-ascorbic acid concentration (193.2mg/kg).