Effects of stress on body cortisol and reproduction of guppy (Poecilia reticulata)

The effects of stress on body cortisol and reproductive performance of guppy, Poeciliar eticulata, was evaluated on 90 immature female fish (0.29 ± 0.03g body weight). The experiment, carried for 30 days in three replications, included: the control (without any manipulation), handling stress (daily holding in a net for 2 minutes) and feeding with the cortisol-treated diet (500 mg per kg food). After this period, reproduction was induced by adding male fish to the remaining females in each tank. No significant difference was observed in growth rate among the treatments (p=0.001). The mortality rate and body cortisol content in both handling and cortisol-fed treatments were significantly higher than that in the control group (p=0.000). The minimum and maximum number of embryos was observed in the control and cortisol-fed groups, respectively. Our results indicated that such manipulations have negative effects on survival and reproductive efficiency and change whole-body cortisol content. Therefore, the measurement of whole-body cortisol content could be a suitable criterion for determining physiological condition in small laboratory fishes.