Assuming the energetic cost of osmoregulation is minimized in an isosmotic medium, the energy spared could support a higher growth rate of fish. The isosmotic point of juvenile mullet Mugil platanus was estimated at 414 mOsmol/Kg H2O, which corresponds to salinity 12‰.The aim of this study was to investigate the effect of salinity on the performance of juvenile mullet reared at different salinities.
Four hundred and eighty fish (0.48±0.01g and 3.27±0.01cm) were randomly distributed into 16 tanks (50L). These tanks were connected to four recirculating aquaculture systems (RAS) equipped with UV sterilization, mechanical and biological filtration and temperature controllers. Each RAS was maintained at salinities 0, 6, 12, and 24, equivalent to 0, 50, 100 and 200% of the isosmotic point of M. platanus. During the experimental period (40 days), fish were maintained at 28.2 ± 0.1°C and oxygen saturation was always above 90%. Fish were fed 4 times per day on NRD INVE (50% protein) until apparent satiation. Results were analyzed by analysis of variance (One-Way) followed by Test of Tukey. All analyses were performed with significance level of p<0.05 and were conducted using the software Statistic 6.0.
Salinity did not influence survival of juvenile mullet (p>0.05), nor influenced feed efficiency. However, final weight and specific growth rate were significantly affected at different salinities (p<0.05). Overall survival was above 90% and feed efficiency was y. Fish reared at salinities 12 and 24 grew faster than those reared at lower salinities (Figure 1 and 2)
Results indicated that salinity plays an important role in juvenile mullet growth and that final weight and SGR were maximized when they were reared at salinity equivalent to, or higher, than the isosmotic point
