Salinity influence on growth, osmoregulation and energy turnover in juvenile pompano Trachinotus marginatus Cuvier 1832

The effects of salinity on growth and parameters related to osmoregulation and energy turnover were evaluated in juvenile pompano Trachinotus marginatus. In a first experiment, fish were reared at different salinities (4, 8, 12, 16 and 20 ppt) for 15 days. No fish mortality was observed. Also, no significant difference in fish size (length and weight), hematocrit and plasma glucose concentration was observed among treatments. Although a significant increase in plasma Na+, Cl- and K+ concentrations was noted with increasing water salinities, while no significant changes in plasma osmolality were observed. The isosmotic point was calculated as 357.5 mOsm/kg H2O, corresponding to the osmolality of the ambient water at salinity 13.1 ppt. These findings indicate that juvenile pompanos T. marginatus acclimated to 20 ppt are fully acclimated to a wide range of salinities (4-20 ppt) after 15 days of transfer to the new salinity condition. Also, they show that the plasma isosmotic point of juvenile T. marginatus (13 ppt) is within the range of values reported for some euryhaline teleost fish from different habitats (10-14 ppt). In a second experiment, fish were reared at different salinities (3, 6, 12 and 32 ppt) for 28 days. No significant difference in survival, feed conversion, Fulton's condition factor, body weight coefficient of variation, feed intake and intestinal trypsin activity was observed among salinity treatments. However, fish reared at 32 ppt showed lower body weight, specific growth rate, oxygen consumption, and gill Na+, K+-ATPase activity than those reared at 3 and 6 ppt. Also, their gills showed higher chloride cell area, epithelium thickness, chloride cell density and mucous cell density than those of fish reared at 3, 6 and 12 ppt. These findings indicate that juvenile pompano T. marginatus is euryhaline in the range of salinities tested (3-32 ppt) and grows better when reared at low salinities (3-6 ppt) for 28 days. This performance is associated with a good osmoregulatory ability resulting from structural and biochemical adaptive responses of the gill epithelium to salinity changes paralleled by increased aerobic metabolism and elevated use of liver carbohydrate store. Although it would be cost effective to maintain higher salinities in coastal aquaculture systems given the proximity to the marine environment, our findings support the idea of rearing juvenile pompano T. marginatus in low salinities (3-6 ppt) to improve growth. Statement of relevance: Pompano rearing performance is improved in low salinities. (C) 2016 Published by Elsevier B.V.