Behavior and histopathology as biomarkers for evaluation of the effects of paracetamol and propranolol in the neotropical fish species Phalloceros harpagos

Pharmaceutical drugs in the aquatic environment can induce adverse effects on nontarget organisms. This study aimed to assess the short-term effects of sublethal concentrations of both paracetamol and propranolol on the fish Phalloceros harpagos, specifically light/dark preference, swimming patterns, skin pigmentation, histopathology, and liver glycogen levels. Fish were acutely exposed to sublethal concentrations of both paracetamol (0.008, 0.08, 0.8, 8, 80 mg L−1) and propranolol (0.0001, 0.001, 0.01, 0.1, 1 mg L−1) under controlled conditions. For scototaxis, a significant preference for the dark compartment was observed for the group exposed to the highest concentration of paracetamol (80 mg L−1). Propranolol exposure significantly altered the swimming pattern, especially in fish exposed to the 0.001 mg L−1 concentration. Pigmentation was reduced in propranolol-exposed fish (0.1, 1 mg L−1). The lowest concentration of propranolol (0.0001 mg L−1) induced a decrease of histochemical reaction for hepatic glycogen. These data demonstrate that pharmaceuticals can induce sublethal effects in nontarget organisms, even at low concentrations, compromising specific functions of the individual with ecological relevance, such as energy balance and behavior.