LERNER, D.T.*; MCCORMICK, S.D.; University of Massachusetts, Amherst; University of Massachusetts, Amherst: Effects of nonylphenol on larval survival and smolt development of Atlantic salmon, Salmo salar

Nonylphenol (NP) is widely found in effluents from sewage treatment plants and industrial sites due to its wide use in detergents, plastics, commercial cleaning products, and pesticide applications. Our previous research has shown that injection of NP in smolts disrupts normal smolt development through endocrine pathways. In this study, the effects of environmentally relevant concentrations of aqueous NP on larval survival and smolt development of Atlantic salmon were examined. Fish were exposed for three weeks to high (100 &micro g/l) or low (10 &micro g/l) concentrations of NP, 17 &beta -estradiol (E₂, 2 &micro g /l), or vehicle as yolk-sac larvae or smolts and were then assessed for gonad maturation, endocrine and osmoregulatory disruption of smolt development, salinity tolerance, seawater feeding and growth, and mortality. Fifty percent of larvae treated with high NP succumbed to mortality by the end of the three-week exposure with less than 5% mortality in the other groups. Between one and two months post-treatment, larvae in the E₂ and low NP groups exhibited 4 and 5 times greater mortality than controls respectively, suggesting a delayed mortality effect. Fifteen months post-treatment, E₂ and low NP groups had a lower proportion of mature male parr than control fish. There were no mortalities of smolts exposed to high NP, low NP, or E₂, indicating smolts were less sensitive than larvae. Smolts treated with either low or high NP, or E₂ exhibited 40-60% increases in plasma cortisol when challenged with a handling stressor. These results indicate that environmentally relevant levels of aqueous nonylphenol can cause immediate and delayed mortality in Atlantic salmon yolk-sac larvae and can affect the hypothalamic-pituitary-interrenal axis of smolts.