Sewage effluent biomonitoring. II. Biochemical indicators of ammonia exposure in channel catfish

Channel catfish (Ictalurus punctatus) were exposed, in situ, to sewage effluent for 17 days to determine the effect of unionized ammonia (UIA) on concentrations of glutamate, glutamine and alpha-ketoglutarate (alpha-KGA) in brain tissue, and activity of glutamate dehydrogenase (L-GDH) in liver tissue. Fish were held in cages either 600 m upstream (0.005 +/- 0.001 mg/liter as UIA, means +/- SE, n = 6) or 9 km downstream (0.032 +/- 0.004 mg/liter, means +/- SE, n = 6). The mean concentrations in micromoles per gram wet weight (means +/- SE, n = 27-30) for glutamate, glutamine, and alpha-KGA at the upstream location were 3.04 +/- 0.29, 5.76 +/- 0.29, and 0.003 +/- 0.01, respectively. Mean concentrations in micromoles per gram wet weight (means +/- SE, n = 27-30) for glutamate, glutamine, and alpha-KGA at the downstream location were 3.03 +/- 0.29, 4.60 +/- 0.37, and 0.02 +/- 0.004, respectively. Mean L-GDH activity in units per milligram protein (means +/- SE, n = 28-30) at the upstream and downstream locations were 0.095 +/- 0.003 and 0.092 +/- 0.003, respectively. Neither the concentrations of these three brain tissue substrates, nor L-GDH activity were significantly different between fish at the two locations even though the observed UIA concentrations were equivalent to concentrations which have been observed to increase glutamine concentration in brain tissue of catfish during exposures under laboratory conditions. Therefore, under the observed field conditions these parameters were not useful biochemical indicators of exposure to potentially detrimental concentrations of UIA.