GROWTH PERFORMANCE OF TARPON Megalops atlanticus IN DIFFERENT OSMOTIC CONDITIONS: IMPLICATIONS FOR OSMOREGULATION AND STRESS

Megalops atlanticus is a marine fish that inhabits Atlantic Ocean, from Bermuda to Brazil. Fish are exploited in fisheries and aquaculture. In recent years in Colombia Caribbean Sea, tarpons began in earthen ponds alone or  in polyculture with other euryhaline species. To fattening, juveniles are captured from the wild and transferred to rearing systems in the swamp called Ciénaga Grande de Santa Marta (CGSM) in Magdalena. Several studies funding the hypothesis that there are very low energy costs in ionoregulation between isosmotic environments, thus the excess energy could be used for fish growth. The main purpose of this study was to survey the range to which juveniles of M. atlanticus was able to regulate electrolyte concentrations, growth performance, survival rates, glucose, ion concentrations and proximal muscle composition in a series of brackish conditions. For this aim, one hundred and eleven fish were caught in estuarine waters near to CGSM and quickly transferred to the Aquaculture Laboratory (Universidad del Magdalena) where they were acclimated during 15 days in tanks of 500 l. Fish were exposed abruptly to three experimental salinities (0, 15, 30 UPS, with three replicates by trial) and maintained in plastic tanks under a RAS condition during three months. Fish were fed daily with fresh fish and progressively accustomed with a moist diet (fresh fish and commercial diet, 30%:70%). Preliminary results showed that there were significative difference between trials (P< 0.05). Salinities influence the effect on fish performance and stress levels. Best condition were observed in fish kept in freshwater. Higher salinity environment influenced poor condition in Tarpon juveniles.