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The temporal patterns of whole body cortisol, the onset of the primary stress response and mRNA abundance of the two glucocorticoid receptors isoforms during early ontogeny was investigated for the first time in the European sea bass, Dicentrarchus labrax . The ontogenetic profile of basal cortisol content was similar to that observed in other pelagic marine species, with minimum values at hatching (0.12 ± 0.01 ng g −1 ), a slight increase at first feeding (2.44 ± 0.71 ng g −1 ) and a first peak at flexion (47.91 ± 6.72 ng g −1 ). However, basal cortisol content at flexion and at the more advanced developmental stages was one of the highest reported for fish. Exposure to a physical stressor (high currents) increased whole body cortisol above control levels at all developmental stages examined (first feeding, pre-larvae, flexion, post flexion, end of metamorphosis and juveniles). However, the magnitude of the cortisol response was low at first feeding and high in juvenile fish. There was a greater number of GR-1 than GR-2 transcripts levels in embryos, pre-larvae and larvae of European sea bass. GR-1 transcripts showed minimum mRNA abundance in embryos and at post flexion and maximum at the end of metamorphosis and in juveniles. The mRNA transcript levels of GR-2 showed a slight increase at hatch to reach a peak in post flexion larvae and in juveniles but these differences were not statistically significant. These results indicate that the onset of cortisol production in European sea bass is near the transition from endogenous to exogenous feeding and show that fish are capable of a stress-induced stimulation of cortisol production even at first feeding. |
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