Renal function in the freshwater rainbow trout (Oncorhynchus mykiss) following acute and prolonged exposure to waterborne nickel

Renal function was investigated in adult rainbow trout following acute and prolonged exposure to waterborne Ni in moderately hard Lake Ontario water (∼140 mg L−1 as CaCO3). Fish were exposed for 36 days to a sublethal concentration of 442 μg Ni L−1, followed by 96 h of exposure to 12,850 μg Ni L−1 (approximately 33% of the 96 h LC50). Prolonged exposure markedly affected only the renal handling of Ni, with no substantial effect on the plasma concentration, urinary excretion rate (UER) or clearance ratio (CR) of Na+, Cl−, K+, Ca2+, Mg2+, inorganic phosphate (Pi), glucose, lactate, total ammonia (Tamm), protein and free amino acids (FAA). Glomerular filtration rate (GFR) was reduced by 75% over 96 h of acute Ni challenge in both fish previously exposed to Ni and naïve fish, with no significant change in urine flow rate (UFR), suggesting a substantial reduction in water reabsorption to maintain urine flow and water balance. Renal Mg2+ handling was specifically impaired by acute Ni challenge, leading to a significantly increased UERMg2+ and significantly decreased plasma [Mg2+] only in naïve fish. Previously-exposed fish were well-protected against Ni-induced Mg2+ antagonism, indicating true acclimation to Ni. Only in naïve, acutely challenged fish was there an increased UER of titratable acidity (TA-HCO3), net acidic equivalents, Pi, Tamm and K+. Again, all of these parameters were well-conserved in previously-exposed fish during acute Ni exposure, strongly suggesting that prolonged, sublethal exposure protected against acute Ni-induced respiratory toxicity.