Abstract

The Australian redclaw crayfish, Cherax quadricarinatus (von Martens), was introduced into Louisiana as a potential species tor soft-shell production, and tor pond production when red swamp crayfish (Procambarus clarkii (Girard)) are not normally produced (June through November). Because of cold-weather limitations, a winter hatchery production period is required to raise juvenile redclaw for spring pond stocking. Good water quality in hatchery systems is essential for the production of healthy juveniles. Total ammonia-nitrogen (NH₃ & NH₄+) and nitrite (NO₂·) are two common pollutants affecting survival and growth of juveniles in recirculating systems. This experiment was designed to evaluated the acute toxicity of ammonia and nitrite to juvenile redclaw crayfish. Juvenile redclaw (0.7 ± 0.2 g, 30.6 ± 3.2 mm) were exposed to a series of ammonia concentrations as NH4CI and nitrite solutions as NaNO₂ at 24 ± 10c (pH 8.6 ± 0.1), to determine the median lethal concentration (LC₅₀). The static-renewal method was used in this experiment. The 24, 48, 72, and 96-hour LC₅₀s of total ammonia-nitrogen (TAN) to juvenile redclaw crayfish were 46.6, 25.7, 20.9, and 16.8 mg L^-1, respectively. These values represent 8.1, 4.5, 3.6, and 2.9 mg L^-1 unionized ammonia-N (UAN) at a pH of 8.6 and a temperature of 24°C. The 24, 48, 72, and 96-hour LC₅₀s of nitrite to juvenile redclaw crayfish were 8.6, 7.2, 6.0, and 4.7 mg L^-1 nitrite-N. Compared with red swamp crayfish and penaeid shrimps, redclaw crayfish are relatively tolerant to ammonia, but sensitive to nitrite pollutants.

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