Effects of fenvalerate on larval development of Palaemonetes pugio (holthuis) and on larval metabolism during osmotic stress

Larvae of the estuarine grass shrimp, Palaemonetes pugio, were reared in the laboratory from hatch through metamorphosis under optimal salinity conditions (20‰) in a range of lethal and sublethal concentrations of the pyrethroid insecticide, fenvalerate. A nominal concentration of 3.2 ng fenvalerate/l significantly reduced the percentage of larvae that completed metamorphosis. Oxygen consumption rates were significantly higher for larvae exposed to this lethal concentration for only 24 h. Exposure to a sublethal concentration of 1.6 ng fenvalerate/l prolonged the duration of complete larval development.Acute osmotic stress modified the metabolism of larval P. pugio reared in sublethal fenvalerate concentrations of 0.1 and 0.2 ng/l and these metabolic responses varied with stage of development. After 8 days of exposure to fenvalerate, oxygen consumption rates were elevated when larvae were exposed acutely to hypoosmotic stress (10‰ S). Metabolic responses of premetamorphic larvae to hypersomotic stress (30‰ S) were also modified by sublethal fenvalerate exposure. Alterations in metabolic-salinity patterns of larval grass shrimp developing under sublethal concentrations of fenvalerate suggest reduction in the ecological fitness of this sensitive life stage by limiting their capacity to adapt to the fluctuating salinity conditions of estuarine waters.