Interactive effects of salinity on oxygen consumption, ammonium excretion, osmoregulation and Na+/K+-ATPase expression in the bullseye puffer (Sphoeroides annulatus, Jenyns 1842)

A physiological study was performed to explore the effects in Sphoeroides annulatus (Jenyns 1842) juveniles of exposure to different salinities 10, 17, 23, 29, 35 and 41‰ on oxygen consumption rate (OCR), ammonium excretion rate (AER), the oxygen-nitrogen atomic ratio (O:N), osmoregulation and Na+/K+-ATPase expression. The OCR values ranged from 27.9 to 30.9 mg O2 h−1 kg−1, displaying a Type 1 response pattern Kinne (1977). AER ranged from 0.60 to 0.69 mg h−1 kg−1, and O:N values were from 53.12 to 59.26, indicating that the puffers use proteins and lipids as an energy-substrate. Osmoregulation in S. annulatus was hyposmotic in salinities of 23, 29, 35 and 41‰ and hyperosmotic in a salinity of 10‰. The isosmotic point of the bullseye puffer was 356 mmol kg−1 (10.5‰). The enzyme expression analysis indicates that the fish acclimated to 41‰ had the highest Na+/K+-ATPase expression level, whereas, the lowest expression level was found close to the isosmotic point. Na+/K+-ATPase expression in the gills was found to have a U-shaped relationship with environmental salinity. We conclude that the bullseye puffer is strongly euryhaline and can be cultivated in a wide range of environments that has important economic implications.