Changes of growth, food intake and cortisol plasma in juvenile carp (Cyprinus carpio) following cortisol injection

The present study conducted to investigate the effect of cortisol injection on growth index، food intake and plasma cortisol in juvenile common carp (Cyprinus carpio). After 2 weeks adaptation، 240 fish with 19. 5 ± 0. 2 g average weight were randomly distributed in to 12 fiberglass tanks with four treatments and three replicates (20 fish per tank). Based on body weight، cortisol (mixed with oil) was injected to treatments with different dosages at 0 (C0)، 1 (C1) and 10 µg/g (C10). At the end of 21 days، fish were weighed and growth parameters showed significantly reduced in C10 (P<0. 05). No significant change was observed in hepatosomatic index among different treatments (P>0. 05). Food intake were recorded daily during the experiment and significantly showed reduction in days 1 to 7، 16 and 19 in C10 compared to control group (P<0. 05). Blood was taken to determine plasma cortisol at the start، day 3، day 7 and day 21 after the experiment. Cortisol concentrations showed significant reduction in C10 compared to C0 group three days after the experiment (P<0. 05). The results showed that increasing of cortisol in a short time after injection، affected by changes of blood plasma cortisol and reduced food intake could negatively have an effect on growth.