Influence of pH, Salinity, Calcium, and Ammonia Source on Acute Ammonia Toxicity to Golden Shiners, Notemigonus crysoleucas

Holding fish at elevated densities with limited water exchange can produce situations where ammonia concentrations are acutely elevated. Ammonia accumulation is considered a major density‐limiting factor during transport and holding of golden shiners, Notemigonus crysoleucas , but unionized ammonia (UIA) toxicity to golden shiners has not been studied in detail. Studies were undertaken to examine 48‐ and 72‐h UIA toxicity to golden shiners in response to ammonia source, pH, calcium concentration, and salinity. Shiners were exposed to geometrically increasing increments of UIA under selective environmental conditions, and monitored for mortality within 48 and 72 h. Probit regression was used to calculate median and 1% lethal concentrations of UIA to golden shiners. No difference in toxicity of ammonium chloride salt or aqueous ammonia hydroxide to golden shiners was found. UIA toxicity to golden shiners was much greater than previously reported, and increased as pH increased (72‐h LC 50 : 1.26 mg/L UIA at pH 7; 0.75 mg/L UIA at pH 8; 0.71 mg/L UIA at pH 9). An increase in environmental calcium (75 mg/L) decreased the toxicity of UIA to shiners by 21.7% at pH 8, whereas salinity had no effect on UIA toxicity. To limit golden shiner losses caused by UIA toxicity, calcium chloride should be added to water sources that contain <100 mg/L hardness, and vats and holding tanks should be flushed if UIA concentrations approach 0.13 (pH 7), 0.11 (pH 8), or 0.10 (pH 9) mg/L at 48 h or 0.12 (pH 7), 0.08 (pH 8), or 0.07 (pH 9) mg/L after 72 h.