Metabolic demand and growth of juveniles of Centropomus parallelus as function of salinity

The effect of salinity and time of exposure on metabolism and growth of juveniles of fat snook, Centropomus parallelus, were investigated. Food conversion efficiency (FCE), specific growth rate (SGR), oxygen consumption, ammonia excretion rate and O:N (oxygen/nitrogen) ratio were assessed on groups of fat-snook (mean weight 2 g) acclimated for 15- and 30-day periods, to 5‰, 20‰ and 30‰ salinities. For 15-day period, differences between FCEs as well as SGRs at different salinities were not significant. For 30-day period, however, these differences were significant between 5‰ and the other salinities, with the highest and lowest values at 5‰ and 30‰, respectively, for both parameters. Salinity and acclimation period exerted significant influence on the oxygen consumption, ammonia excretion and the O:N ratio of juveniles of C. parallelus. The lowest and highest oxygen consumption was at 20‰ for 15- and 30-day period, respectively. Differences in oxygen consumption between fishes maintained at 5‰ and at 30‰ were not significant, at each period, while between those maintained at 5‰ and 20‰, and at 20‰ and 30‰ differences were significant. Ammonia excretion rates were significantly different between all salinities, at each period, and between periods at each salinity, except at 30‰. The highest and lowest rates were found at 5‰ and 30‰, respectively. The highest O:N ratio for 15-day period was at 30‰ with no difference between those at 5‰ and 20‰. For 30-day period, differences of O:N ratio were significant between salinities. The effect of acclimation period on the O:N was significant only at 20‰. Although C. parallelus is a fish species adapted to face a wide variation of environmental salinity, results show that juvenile fishes kept at different salinities, in laboratory, found better condition to efficiently channel the energy of food into growth at 5‰ for both acclimation periods.