The effects of salinity and temperature on growth and survival of Australian snapper, Pagrus auratus larvae

The effects of salinity and temperature on performance were determined for Australian snapper, Pagrus auratus first-feeding to pre-metamorphosis larvae held in 100-l recirculation tanks. In the first experiment, performance was assessed after transfer from 35‰ at eight salinity treatments (5‰, 10‰, 15‰, 20‰, 25‰ 30‰, 35‰ and 45‰) in larvae from 3 to 21 days after hatching (dah). Survival of larvae was best within the range of 20-35‰. Final size of larvae was similar within the range of 10-35‰ (6.8 ± 0.1 to 7.1 ± 0.2 mm total length [TL]; 3.0 ± 0.3 to 3.3 ± 0.3 mg wet weight) but larvae were 15% shorter at 45‰. Final swimbladder inflation and feeding onset of larvae was not affected by salinity in the range of 10-45‰. The presence of calculi in the urinary bladder of larvae was correlated positively with increasing salinity but no relationship between urinary calculi and larval survival was observed. In a second experiment, performance was assessed after transfer from 21 °C at seven temperature treatments (15, 18, 21, 24, 27, 30 and 33 °C) in larvae from 3-21 dah. All larvae transferred from 21 °C to 30 °C and 33 °C died after 3 days and from 21 °C to 27 °C died after 9 days. Survival was not significantly different between 15 °C and 24 °C. Larval growth increased as temperature was increased; larvae at 24 °C (4.8 ± 0.2 mg wet weight) were 6-fold heavier than larvae at 15 °C. Swimbladder inflation of larvae grown at 18 °C, 21 °C and 24 °C was high (65.2 ± 18.0% to 86.7 ± 8.8%) and similar but inflation was lower in 15 °C and 27 °C. The incidence of urinary calculi occurred earlier and in a greater number of larvae when temperature was increased. Feeding onset was not affected by temperature. In a third experiment, performance was assessed at combinations of two salinities (20‰ and 35‰) and three temperatures (18 °C, 21 °C, and 24 °C) in larvae from 3 to 24 dah. Survival of snapper larvae was not significantly different between these treatments. Growth was not affected by salinity but larvae increased in size as temperature was increased and there was no interaction of salinity and temperature. The percentage of larvae that commenced feeding and inflated their swimbladders was similar in all treatments. Salinity and temperature influenced the incidence of urinary calculi and there was an interaction between the parameters. Based on our results in terms of larval performance (growth), development and survival, we conclude that the optimal conditions for larval rearing of snapper from first-feeding (3 dah) to pre-metamorphosis (24 dah) are combinations of salinity from 20‰ to 35‰ and a temperature of 24 °C.