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o (~I N ,.,:::. (\) f.J characteristics including DO were measured weekly in all exposure aquaria as described above. During the progeny residue study, the same water quality parameters were measured twice in three exposure aquaria. Water temperature in the progeny studies was monitored daily in one aquarium using a mercury thermometer. Selenium Analyses Total selenium concentrations in water, diet, eggs, and larvae were determined by hydride generation atomic absorption spectroscopy (HGAAS) using a Perkin-Elmer Corporation (Norwalk, CT) model 3300 atomic absorption spectrophotometer equipped with a model MHS-lO mercury hydride generator. Operational procedures for HGAAS closely followed those ." of Perkin-Elmer (1978, 1982), Water samples were thawed under refrigeration and then subjected to a two-step digestion procedure modified from Presser and Barnes (1984). Briefly, the samples were prepared for analysis by adding 1 m] of 5% potassium persulfate and 0.4 ml of instra-analyzed HCl (J.T Baker) to 20 ml of sample in a 100-ml beaker. Duplicate digestions were performed on each sample. The samples were digested on a hotplate and the digestate was diluted to 100 ml with 8% HCl prior to analysis. Each digestate was analyzed in duplicate and the meim concentration recorded. Duplicate samples of the diet, eggs, and larvae were freeze dried to a constant weight for moisture determination using a Virtis (Gardiner, NY) 3-L vacu-freeze condenser sentry system. The dried samples were placed in 1 aO-ml beakers and subjected to a combined nitric acid wet digestion and magnesium nitrate dry ash procedure (Siu and Berman 1984). The digestates were diluted to 100 ml with 10% HCl prior to analysis, Each digestate was analyzed in duplicate and the mean concentration recorded. 20