MCCORMICK, S.D.; BJ�RNSSON, B.T.; MOECKEL, A.M.; LERNER, D.T.; O’DEA, M.F.: Endocrine pathways for the disruption of the parr-smolt transformation by estradiol and nonylphenol.

Sex steroids are known to interfere with normal development of the parr-smolt transformation, and environmental estrogens such as nonylphenol have recently been implicated in reduced returns of Atlantic salmon in the wild. In this study juvenile Atlantic salmon were injected with 0.5, 2, 10, 40 and 150 ug/g branched 4-nonylphenol and 2 ug/g estradiol-17 during the parr-smolt transformation in April and sampled 1 and 2 weeks after first exposure. Estradiol and 150 ug/g nonylphenol resulted in lower salinity tolerance and decreased plasma IGF-I. Plasma growth hormone was elevated at intermediate doses of nonylphenol, but there was no effect of higher doses. There was no effect of estradiol on plasma growth hormone. Plasma cortisol was not affected by nonylphenol or estradiol. Plasma thyroxine showed a strong dose dependent decrease in response to nonylphenol and estradiol. The results indicate that plasma IGF-I is the likely endocrine pathway for the effects of estrogenic compounds on osmoregulation, and that plasma thyroxine is negatively affected by nonylphenol at relatively low doses.