Effect of stress severity on zebrafish (Danio rerio) growth, gonadal development and reproductive performance: Do females and males respond differently?

The current trial was carried out to examine the impacts of stress on growth, gonadal development, and reproductive performance in both sexes of zebrafish. In these experiments, adult fish were distributed in nine aquaria and were held for 42 days. Trial treatments included: 1) NCN group (no daily chasing or netting), 2) 1CN group (once a day chasing and netting both for 1 min during 42 days), and 3) 2CN group (twice a day chasing and netting both for 1 min during 42 days). Growth performance, gonadal development and reproductive performance were assessed. After 42 days the fish were sacrificed to allow for the determination of cortisol levels and for histological analysis of the gonads. Female zebrafish in NCN group showed higher growth performance than the stressed groups (P < .05) but no significant differences were found between males in the NCN group and stressed groups (P > .05). Cortisol levels were highest in male zebrafish in 1CN and lowest in males from the NCN groups. Moreover, the highest and lowest female cortisol levels were found in 2CN and NCN treatments, respectively (P < .05). Histological analysis of gonads of the 2CN groups showed that oocytes and testis were in the vitellogenesis and mid-spermatogenesis stages, respectively. Fish in the 2CN groups had a lower latency time to ovulation and NCN group produced more embryos than the other groups (P < .05). These results suggest that chronic stressing events tend to depress growth in both sexes, and reproductive performance in females.