Background. Increasing global usage of inorganic fertilizers, including phosphate-based fertilizers has its negative consequences on the aquatic environment. Effects of single superphosphate fertilizer (SPF) remain unknown, particularly its influence on the respiratory dynamics of fish under continuous exposure. We investigated the effects of single SPF on the survival and respiratory dynamics of Nile tilapia, Oreochromis niloticus, under laboratory conditions. Materials and methods. Nile tilapia fingerlings (of mixed sex) (5.40 . 0.03 g) were exposed to various concentrations of the fertilizer in five treatment regimes (in triplicate): 0.88, 1.75, 3.50, 7.00, 14.00 g . L–1 (and 0.00 g . L–1 for control). Each replicate was carried out in a 30-L circular plastic tank based on 20 fingerlings. The study involved: the mortality estimation, the oxygen consumption, the histopathological effects on fish gills, and the activities of lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH) in liver of fish exposed to sublethal concentrations (0.44, 0.22, 0.11, 0.06, and 0.03 g . L–1) of single SPF for eight weeks under laboratory conditions. Results. Acute concentrations of SPF had serious adverse effects on mortality, oxygen consumption and opercular ventilation rates of exposed fish. All variables showed a dose-dependency. A mean value of 96-h LC50 of the SPF to the test fish was calculated to be 3.76 g . L–1. At various acute concentrations, oedema and hyperplasia of gill lamellae were observed in exposed fish. Exposure of the fish to sublethal concentrations of the SPF resulted in reduction in the levels of lactate dehydrogenase and alcohol dehydrogenase activities in liver. Conclusion. Concentrations of SPF in natural water bodies are deleterious to aquatic fauna. With rapid global economic development and need for more food production, pollution from agricultural fertilizers remains a major threat to the aquatic ecosystem. Therefore it is ultimately important that a balance is struck between achieving economic excellence and environmental protection through good pollution management strategies.

Oreochromis niloticus, single superphosphate, dose-dependency, toxicity, respiratory distress