Insights into salinity effect on growth of the spotted scat (Scatophagus argus): Exploring the optimum salinity for its culture

Salinity is a pivotal abiotic factor affecting growth of aquatic species in the mariculture. As a euryhaline species, the spotted scat ( Scatophagus argus ) can tolerate a wide range of salinity levels and is farmed between brackish to marine water conditions. In the present study, the effect of salinity on growth performance in Scatophagus argus juveniles was evaluated and analyzed. After a 12-week experimental period, the average body weight of S. argus juveniles was significantly different ( p < 0.05) in six salinity treatments (5, 10, 15, 20, 25, and 30 ppt). Feed intake (FI) was increased with the enhancement of environmental salinity, and its highest value (1.51 ± 0.11) was found in 30 ppt group. However, the growth performance was not consistent with food intake, and the highest value of the average body weight (89.4 ± 6.9 g) was recorded in fish reared at an intermediate salinity (15 ppt) by the end of the experimental period. The results above indicated that there were energetic trade-offs between osmoregulation and somatic growth. A “U-shaped” relationship between salinity and final weight was revealed through regression analysis, and it was deduced that the optimal salinity for the growth of S. argus juveniles was 17.40 ppt. The polynomial regression equation between body weight and environmental salinity was y = 56.28 + 3.48x–0.01x 2 . GH and IGF-I levels in the plasma of S. argus juveniles were increased from the fourth week to the end of experiment. Their values under hyperosmotic conditions (15, 20, 25 and 30 ppt) were significantly higher than those under hypoosmotic and isosmotic conditions (5 and 10 ppt), which indicated GH and IGF-I levels was associated with the environmental salinity. As for cortisol, a hormone that is involved with salinity adaption and metabolism, its level was kept relatively stable in each group during the experiment. However, significant contrasts were found in cortisol levels between these groups, and at each timepoint, its highest level was observed in 30 ppt salinity group. As for GH and IGF-I, their highest values were recorded at 15 ppt, rather than 30 ppt, from the fourth week to the end of experimental period. Based on these results above, GH/IGF-I and cortisol variations reflected a balance between salinity adaptation and somatic development in S. argus juveniles. In view of endocrine modulation, the somatic growth of S. argus juveniles was modulated by cross-talk interactions between GH/IGF-I and cortisol under different salinity conditions. • The optimal salinity for the growth of Scatophagus argus juveniles was deduced to be 17.40 ppt. • There were energetic trade-offs between osmoregulation and somatic growth in Scatophagus argus juveniles. • The growth was modulated by cross-talk interactions between GH/IGF and cortisol under different salinity conditions.