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Water quality in five southern Louisiana commercial crawfish (Procambarus clarkii and P. acutus acutus) ponds was monitored from November 1982 through May 1983. Two ponds were planted with rice (Oryza sativa) and three ponds had volunteer terrestrial and semi-aquatic vegetation as crawfish forage.

Water quality was poorest in November, April, and May when water temperatures exceeded 18"C. However, only dissolved oxygen (DO) attained concentrations low enough (<1.0 mg/liter) to be acutely toxic to crawfish. Free carbon dioxide (CO2) attained levels (12.0 mg/liter) that could potentially harm crawfish during periods of low DO (<2.0 mg/liter). The temperature, pH, free CO2, nitrate, total phosphorus, biochemical oxygen demand (BOD), chlorophyll a, total hardness, and total alkalinity did not differ significantly among rice ponds and ponds with volunteer vegetation. The DO, nitrite, total nitrogen, and chemical oxygen demand (COD) were highest in rice ponds (P<0.05). The soluble inorganic phosphorus (SIP) and conductivity were highest in ponds with volunteer vegetation (P<0.05).

Free CO2, SIP, conductivity, and total alkalinity levels were positively correlated with an increase in macrophytic biomass (P<0.10). Nitrite, total nitrogen, COD, BOD, turbidity, temperature and DO decreased with increased vegetative biomass. Crawfish catch was positively correlated with total ammonia, BOD, COD, and water temperature, and negatively correlated with total phosphorus, total nitrogen, SIP, total alkalinity, and DO.

The toxicity of hydroxyl and hydrogen ions (i.e., pH), ammonia, and nitrite to juvenile P. clarkii was determined in static acute toxicity tests. The 96-hour LC50’s of hydroxyl and hydrogen ions to P. clarkiiwere 10^-3.88 moles OH /liter (pH 10.12) and 10^-3.21 moles H /liter (pH 3.21). The 96-hour LC50’s of ammonia and nitrite to P. clarkii were 2.65 mg NH3-N/liter and 5.94 mg N02-N/liter, respectively.