EFFECTS OF DIFFERENT DIETARY VITAMIN C LEVELS ON CHINESE LONGSNOUT CATFISH (LEIOCASSIS LONGIROSTRIS GUNTHER)
饲料中不同维生素C含量对长吻鮠的影响

Vitamin C is an essential micro-nutrient for most fish and plays an important role in immunity and physiology. The deficiency of dietary vitamin C can result in the damage on fish. The study on the deficiency symptom and the sensitive indicator of vitamin C could provide useful information for fish feed industry. This experiment was conducted to investigate the effects of dietary Vitamin C levels on growth performance, immune and physiological responses in Chinese longsnout catfish (Leiocassis longirostris Günther), which is an high value aquaculture fish in China. Three practical diets containing 38, 364 and 630 mg/kg vitamin C were fed to Chinese longsnout catfish (23.19±0.58g) for 8 months. Vitamin C was used in the form of L-ascorbyl-2-polyphosphate. The results indicated that the Chinese longsnout catfish in 38mg/kg vitamin C groups showed typical vitamin C deficiency symptom: skin color turning darker, spinal deformities and scoliosis, erosion of fins, anaemia. SGR and the serum lysozyme activities decreased significantly (p<0.05), the hepatic SOD activities and MDA contents increased significantly (p<0.05). There was no significant difference in serum cortisol concentrations (p>0.05). The inductive HSP70 in liver was not detected by western-blotting in all groups. In conclusion, serum cortisol and hepatic HSP70 were not the sensitive indicators for vitamin C deficiency symptom, but the serum lysozyme, hepatic SOD activity, hepatic MDA content and the haematological index (red blood cell number and hemoglobin content) were the more reliable makers to indicate the physiological status in Chinese longsnout catfish.