Effect of salinity on the growth of brown flounder,Paralichthys olivaceus and its compensatory growth following salinity manipulation

Brown flounder,Paralichthys olivaceus is an important fishery and aquaculture species. The capacity of tolerating variable salinity is one of the important abilities to survival the different natural or cultural environments. Two experiments were conducted to investigate the effects of salinity manipulating on the growth of juvenile P. olivaceus. In the first experiment,juveniles with an average body weight of 2.6 g were kept in seawater with different salinities (12–S12,19–S19,26–S26,33–S33,40–S40) for 30 d. In the second experiment,juveniles with body weight of 6.9 g were stocked in seawater with salinities 5 (IS5),19(IS19),and 47(IS47) during the first 10 d. Then the salinities were adjusted to 19 in 3 d at a steady rate and the fish experienced a recovery period of 30 d. It was found that the wet weight growth,wet weight feeding rate,and wet weight feed conversion efficiency of juvenile P. olivaceus would not changed significantly within the salinity range between 12 and 40 (P0.05). But salinity put significant effects on these parameters when they were calculated in terms of protein and energy (P0.05). Juvenile P. olivaceus stocked in seawater with salinity 5 (IS5) and 47(IS47) would grow significantly slower than that fish stocked in salinity of 19 (P0.05). Fish in IS5 achieved completely compensatory growth in 30 d after the salinity was switched to 19. But fish in IS47 failed to catch up the weight of fish in IS19. For the whole recovery period (11-40 d),P. olivaceus in IS5 showed significant better appetite than that in IS47 and the appetite of fish in IS19 was in between. After switching of salinity from 5 and 47 to 19 respectively,no significant difference on feed conversion efficiency between treatments appeared during the experimental period (P0.05). Results mentioned above indicated that the compensation of the growth delay caused by low salinity (5) was dependent mostly on improved feeding rate. It could be concluded that the juvenile was expecially tolerant to lower salinity stress.