Efeito da salinidade da água sobre juvenis de pacamã Lophiosilurus alexandri

Abstract

This work aims to evaluate the lethal and sub-lethal effect of different water salinities in pacamã juvenile. In experiment 1, juveniles of weight 28.6 ± 1.3 g and length 12.8 ± 1.8 cm were transferred directly from freshwater to salinities: 0 (freshwater), 2.5, 5.0 , 7.5, 10, 12.5 and 15.0 g of salt/L, in a completely randomized design with seven treatments and three replications and observed for 96 hours. In experiment 2, juveniles of weight 15.5 ± 0.8 g and length 11.0 ± 1.0 cm were subjected to treatments: (0) freshwater, 2.5, 5.0, 7.5 and 10 g of salt/L with three random replications for 28 days. In experiment 1, after 24 hours of osmotic shock, the CL50-24h was estimated at 11.67 g of salt/L and at the end of 96 hours, the survival rate was 100% up to salinity 7.5 g of salt/L, while at 10 g of salt/L was 58.3%. After 24 hours changes in glucose, hemoglobin, osmolarity, hematocrit, cortisol, ALT and Cl- ions were recorded. However, no significant difference was found in total plasmatic protein, triglycerides, cholesterol and albumin (P>0.05). Comparing the data of 24 and 96 hours, hematological and biochemical responses showed mixed results depending on the variable analyzed. In experiment 2, overall mortality at 10 g of salt/L was recorded in the 21th day of experiment. After 28 days, the survival rate was 100% between freshwater and 5 g of salt/L and 18% at 7.5 g of salt/L. In terms of biomass gain and feed conversion were measured quadratic response with higher estimated level at 2.01 and 2.45 g of salt/L, respectively. The weight gain, daily weight gain and specific growth rate showed constants until the estimated values of 2.64, 2.63 and 2.83 g of salt/L, respectively, with reduced values in higher salinity. In whole fish composition, for phosphorus was recorded quadratic response with the highest level estimated for this variables at 3.24 g of salt/L and lower estimate level for the derivative of equation at 0.98 g of salt/L for protein. For energy constant values were found to 2.15 g of salt/L. Comparing the hematological and biochemical data of 24 hours and 28 days, several changes were found considering time of experiment, salinity and also the interaction among these factors, depending on the variable analyzed. Water salinity has direct implications in following variables of L. alexandri juvenile: hematological, biochemical, performance and carcass composition and salinity up to 7.5 g salt/L in short bath period and 2.5 g/L in long period can be used.