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A study of fish from two Texas lakes evaluated hepatic concentrations of selenium. Selenium was nearly four times higher in sunfish from contaminated Martin Lake (7.6 u.g/g) than in fish from a reference lake (2.1 ug/g). Sunfish with elevated levels of hepatic selenium had substantial alterations in the liver, including necrosis, cytoplasmic vacuolation, and Kupffer cell proliferation. The ovaries of mature fish collected from Martin Lake frequently had atretic follicles, abnormally shaped follicles, connective tissue hypertrophy, asynchronous oocyte development, and an overall reduction in the number of developing oocytes. These abnormalities were not detected in the population from the reference lake. This article does not give concentrations in water, sediment, or food, but notes that a reduced amount of selenium is still being discharged into the lake (Sorensen 1988). Lemly (1983) showed that ventilation frequency and pectoral fin activity of bluegills and largemouth bass increased significantly when the selenium water concentration increased from 5 to 10 gg/L. Such effects led to an increased need for oxygen, which demonstrates why selenium's toxicity is greater in colder water (Lemly 1993a, 1997a). 3.1.1 Acute Toxicity Although concentrations of selenium in the environment are seldom acutely toxic, a review of acute toxicity is appropriate because the data provide an estimate of the relative sensitivity of the various species. Acute toxicity data have been reviewed by Mauk and Brown (1999) who made the following comments: "Studies have determined that 96-h LC50 values range from 1 to 35 mg/L for fish species (e.g., Kaaverkamp et al. 1983; Niimi and LaHam 1976; Sato et al. 1980). For coolwater fish species similar to walleye, Kalverkamp et al. (1983) report a 75.5-hour LC50 of 11.1 mg/L for northern pike and a 10-day LC50 of 4.8 mg/L for yellow perch." Those published values were similar to the 12 mg/L 96-h LC50 reported by Mauk and Brown (1999) for walleye. Hamilton and Buhl (1996) reviewed their previous toxicity testing with the pikeminnow and razorback sucker and noted that both species from the Green River were "significantly less sensitive to selenate than to selenite." However, in San Juan River water, the pikeminnow had the same selenate to selenite relationship (the 96-h LC50 values were 88 mg/L for selenate and 20.7 for selenite), but the razorback sucker showed similar sensitivity to both forms (the 96-h LC50 was 15.9 mg/L for selenate versus 11.3 mg/L for selenite). These data suggest that there are unknown factors affecting the toxicity of the selenium species. The selenite 96-h LC50 was similar for the flannelmouth sucker which, like the pikeminnow, showed approximately half as much sensitivity to selenate. 3.1.2 Chronic Toxicity Chronic selenium toxicity to fish remains a controversial issue. One reason is that adult fish can tolerate relatively high levels of selenium in their tissues with no apparent ill effects. Dietary selenium sufficient to load eggs beyond teratogenic thresholds (diet of 5-20 ug/g) does not affect health or survival of parent fish. Apparently adults, because of their lipid reserves and larger livers, can withstand the selenium, but when reproducing, the female draws on these lipid reserves and passes the selenium to her progeny. Hatchability is not affected, but survival of the larvae is severely compromised (Lemly 1998). Tissue concentrations of 6-12 ug/g in fillets and 20-40 ug/g in visceral tissues are sufficient to be presumptive of teratogenesis. This report also