Effects of the Amplitude and Frequency of Salinity Fluctuations on the Growth Performance of Juvenile Tongue Sole (Cynoglossus semilaevis)

The effects of amplitude (2, 4, 6, 8 ppt) and frequency (2, 4, 8 days) of salinity fluctuations on the growth, body composition, and energy budget in juvenile tongue sole (Cynoglossus semilaevis) were investigated for 64 days. Results showed that the frequency and amplitude, as well as the interaction between them, significantly affected the specific growth rate. The tongue sole had higher specific growth rates at the amplitudes of 4 and 6 ppt and frequencies of 4 and 8 days than tongue sole in other treatments or the unfluctuating control. In these treatments, food consumption, food conversion efficiency, and apparent digestion in terms of energy were also significantly higher than in the control. The growth rate of the juvenile tongue sole was a quadratic function of the salinity amplitude at various frequencies and was described by the equation G = beta(0) + beta(1)(SA) + beta(2)(SA)(2), where G represents the specific growth rate on a 64-day basis, SA is salinity amplitude in ppt, beta(0) is the intercept on the G axis, and beta(1) and beta(2) are the regression coefficients, respectively. The optimal salinity amplitudes for the best growth at salinity fluctuation frequencies of 2, 4, and 8 days were estimated to be 3.54, 4.89, and 4.74 ppt, respectively, suggesting that commercial farmers can rear juvenile tongue sole in moderate salinity fluctuations to achieve better growth performance.