Reproductive endocrine variation in female olive flounder with different stress coping styles during the breeding season

Abstract

The hypothalamic–pituitary–inter-renal (HPI) axis activity is related to the stress coping styles of olive flounder, Paralichthys olivaceus. But the relationship between hypothalamic–pituitary–gonadal (HPG) axis activity and stress coping styles remains unknown. Here, we combine physiological measurements with ovarian development to examine the reproduction differences between proactive and reactive flounders. The GSI was significantly higher in the proactive fish than the reactive type during the breeding season. In April, all the proactive fish under investigation had ovaries at mid-vitellogenic stage while reactive fish had ovaries at pre-vitellogenic stage, but both the proactive fish and the reactive ones had ovaries at post-vitellogenic stage in May. In HPG axis, the plasma E2 levels and the mRNA levels of fshβ, fshr and lhcgr was higher in the proactive flounder than the reactive ones in April yet there was no difference between them in May. In HPI axis, the concentration of cortisol was lower in the proactive fish than the reactive ones in April, yet the results indicate no difference in May. Surprisingly, the transcript gr in ovary displays no differences between the proactive and the reactive fish and mr shows significant up-regulation for the proactive fish in April and the results indicated no difference again in May. Overall, these data suggested that the proactive individuals matured earlier than the reactive ones, the activity of HPI axis was lower, and the activity of HPG axis was higher in the proactive fish than the reactive ones during the breeding season.