ALTERATIONS IN THE ENERGY-METABOLISM OF AN ESTUARINE MYSID (MYSIDOPSIS-BAHIA) AS INDICATORS OF STRESS FROM CHRONIC PESTICIDE EXPOSURE

Dose-response relationships were developed for several metabolic rate functions (oxygen consumption and ammonia excretion) and physiological indices (K2 values and O: N ratios) at different life stages of an estuarine mysid (Mysidopsis bahia) during a life-cycle exposure to fenthion, an organophosphate insecticide. Initial exposure to fenthion resulted in elevated respiration rates of juvenile mysids. As shown by lower net growth efficiency (K2 values), these increased metabolic demands reduced the amount of assimilated energy available for production of new tissue, resulting in retarded juvenile growth rates. O : N ratios indicated that juvenile mysids primarily utilized lipid substrates as an energy source, but during maturation shifted to greater usage of proteinaceous substrates. Higher O : N ratios during maturation of fenthion-exposed mysids suggest greater reliance on the more energy-rich lipid substrates to support the elevated rates of oxidative metabolism, resulting in less lipid material being available for gamete production. These results, when compared with similar studies with two other pesticide classes, suggest that measurements of alterations in the energy metabolism of contaminated individuals from sensitive zooplankton populations (e.g. mysids) may be used as indicators of reductions in population performance from chronic exposure to toxic organics. © 1990.