RESUMO
High usage of the synthetic glucocorticoids (GCs) has led to significant presence of this pharmaceutical group in surface waters where it can affect non-target organisms such as fish. Assessment of a fish's metabolism and swimming performance provide reliable sub-lethal measures of effects of GCs on oxygen-requiring processes and ability to swim. In this study, we determined time-dependent (7, 14 and 21 days) effects of the synthetic GC prednisone (1 µg L-1) on sheepshead minnow (SHM) (Cyprinodon variegatus). Standard (SMR), routine (RMR) and maximum (MMR) metabolic rate, metabolic scope (MS), excess post-exercise oxygen consumption (EPOC), cost of transport (COT) and critical swimming speed (Ucrit) were determined. Twenty-one days exposure to prednisone resulted in significantly higher SMR, RMR, MMR, MS, EPOC and COT compared with 7d and 14d prednisone fish. However, Ucrit was not significantly different between prednisone and solvent control exposed fish (within 7d, 14d, 21d groups). SMR, RMR and MMR were lower in the 7d and 14d prednisone exposed fish compared with their solvent control groups. In contrast, SMR, RMR and MMR were all significantly higher in the 21d prednisone exposed fish compared with solvent control. EPOC was significantly higher in 14d prednisone exposed fish and trending higher in 21d and 7d prednisone exposed fish compared with their solvent controls. EPOC was significantly higher in 21d compared with 7d prednisone exposed fish. A significantly higher COT was seen in the 21d compared with 7d and 14d prednisone fish. Collectively, this study showed time-dependent effects of prednisone on SHM metabolism and swimming performance.