Use ofNeomysis mercedis(Crustacea: Mysidacea) for Estuarine Toxicity Tests

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The mysid Neomysis mercedis was examined as a test organism for use in acute toxicity tests at intermediate salinities characteristic of estuarine waters. Several sensitive invertebrate species are available for marine assessments (mysids) and freshwater tests (cladocerans), but few are available for estuarine toxicity tests. Observations in the laboratory indicate that Neomysis mercedis can be reared successfully at a temperature of 17°C, a salinity of 2‰, and a population density less than 5/L. Brine shrimp nauplii Artemia salina, algae, and commercial foods were used to sustain mysid cultures. Neomysis mercedis is viviparous and can complete its life cycle in 3–4 months. Neomysis mercedis is as sensitive as or more sensitive to toxicants than the marine mysid Mysidopsis bahia and the freshwater cladocerans Daphnia magna, Ceriodaphnia dubia, and Simocephalus serrulatus. The mean 96-h LC50 values (concentrations lethal to half the test animals) for N. mercedis, in increasing order, were 0.20 μg/L for methyl parathion, 2.2 μg/L for malathion, 14 μg/L for carbofuran, 150 μg/L for copper sulfate, 280 μg/L for thiobencarb, and 1,600 μg/L for molinate. Neonates (5 d postrelease) were generally more sensitive than older juveniles. Coefficients of variation (100·SD/mean) of LC50 values varied from 21 to 35%.