The impact of elevated water ammonia and nitrate concentrations on physiology, growth and feed intake of pikeperch (Sander lucioperca)

The ammonia (NH3) and nitrate (NO3-) threshold concentrations in rearing water of juvenile pikeperch (Sander lucioperca) were assessed. Pikeperch with an initial mean (SD) weight of 17.7 (4.2) g were exposed to 0.9 (control), 3.6, 5.2, 7.1, 11.2 and 18.9 µM NH3 in the water for 42 days. Plasma NH4+ concentrations stayed at control levels (~ 650 µM) up to 11.2 µM NH3 in the water. At the highest water NH3 concentration tested, plasma NH4+ had more than doubled to 1400 µM. Based on the specific growth rate, the EC10 value for NH3 was 5.7 µM. When pikeperch (initial mean (SD) weight of 27.0 (4.9) g) were exposed to 0.1 (control), 1.5, 2.3, 3.7, 6.1, 10.2, 15.8 and 25.6 mM NO3- for 42 days, mean (SD) plasma NO3- concentrations increased linearly from 88 (47) to 5993 (899) µM at the highest ambient NO3- level. Feed intake, specific growth rate and feed conversion ratio were not affected. Neither NH3 nor NO3- exposure significantly affected haematocrit, plasma concentrations of cortisol, glucose, lactate, osmolality, gill morphology or branchial Na+/K+-ATPase activity in pikeperch. For juvenile pikeperch we advise not to exceed a water NH3 concentration of 3.4 µM (0.05 mg NH3–N/L), the lower limit of the 95% confidence interval of the EC10 value for SGR, to ensure proper physiology and growth. For NO3- we advise not to exceed 25 mM (350 mg NO3-–N/L). This criterion is based on the highest NO3- concentration tested (25.6 mM). As no negative effects were detected at the highest concentration tested, the actual NO3- threshold probably exceeds 25.6 mM.