Effects of salinity and temperature on the growth, survival, whole body osmolality, and expression of Na +/K + ATPase mRNA in red porgy ( Pagrus pagrus) larvae

Abstract

Atlantic red porgy, Pagrus pagrus, is an important reef fish species in the Mediterranean and the snapper–grouper complex off the southeastern United States. Red porgy is a viable candidate for aquaculture with high market value and the ability to spawn freely in captivity. The objective of this study was to examine the combined effects of temperature and salinity on eggs, yolk-sac larvae, and early feeding-stage larvae of red porgy to day 16 post-hatching (d16ph). To determine the optimal temperature and salinity conditions for culture, embryos were reared under four temperatures (17, 19, 21, and 23 °C) and two salinities (24 and 34 g/L) in a 4 × 2 factorial design. Significant effects of temperature and salinity on growth (notochord length, wet and dry weight), survival, whole body osmolality, and expression of Na +/K + ATPase were observed with minimal interactive effects. Under both salinities, growth increased with increasing temperature. On d16ph, wet weights at 21 and 23 °C (2.03 and 2.91 mg, respectively) were significantly higher than at 17 and 19 °C (0.20 and 0.69 mg). Salinity had no effect on growth at any temperature, but had a significant effect on survival to d16ph, with greater survival at 24 g/L (18.4%) than at 34 g/L (6.77%). Salinity significantly affected whole body osmolality on d2ph and d11ph, with 24 g/L having lower whole body osmolality than 34 g/L on both days. Temperature significantly affected whole body osmolality on d6ph, with no clear trends and on d17ph, with 17 °C (534 mOsm/kg) higher than all the higher temperatures (396–411 mOsm/kg). After increasing each tank to 44 g/L to create a sublethal salinity challenge on d16ph, larvae from 34 g/L treatments did not show an increase in levels of Na +/K + ATPase mRNA after 24 or 48 h post transfer. However, fish in the 24 g/L treatments showed a significant increase in expression of Na +/K + ATPase mRNA after 24 h followed by a decrease after 48 h. Within the ranges tested, a temperature of 23 °C and a salinity of 24 g/L appear to be optimal for culture of red porgy embryos, yolk-sac, and first-feeding stage larvae to d16ph.