Stress Modulated Physiological Responses in Nile Tilapia, Oreochromis niloticus, treated with Non-Ascorbic Acid Supplemented Feed
Stress caused by the aquaculture environment hampers normal growth and immune response of fish and makes them susceptible to diseases. Ascorbic acid (vitamin C), on the other hand, has been known to improve the immune response. Experiments were conducted to investigate the effects of the absence of vitamin C in fish dietgrown in stressed condition induced by crowding. Fish fingerlings were obtained from a local fish farm and were acclimated in the new environment for two weeks. After the acclimation period, fish were maintained in two different conditions: controlled and stressed (density > 50 g/l). Within each condition, fish were further divided into two diet groups, each with two replicates. The experimental groups were fed vitamin C supplemented (1000 mg/kg) feed and the control groups were fed vitamin C free feed for fifteen days. Six fish from each group were sampled to assess the physiological parameters: plasmacortisol, blood glucose, plasma protein, packed cell volume, spleen somatic index, and condition factor. Fish in the stressed conditions showed significantly higher level (p<0.05) of plasma cortisol, blood glucose indicating stress, both of which were reduced when fed vitamin C supplemented diet. Significantly higher (p<0.05) hematocrit concentration was observed in the vitamin C fed group indicating better physiological adaptation.