Acute hyperosmotic stress test for vigor assessment of first-feeding larvae of spotted sand bass Paralabrax maculatofasciatus and spotted rose snapper Lutjanus guttatus

This study investigated the tolerance of first-feeding larvae of spotted sand bass Paralabrax maculatofasciatus and spotted rose snapper Lutjanus guttatus to acute hyperosmotic stress. P. maculatofasciatus and L. guttatus embryos were incubated in 48-well microplates at 23 and 28°C, respectively. The first-feeding larvae were exposed in triplicate to salinities of 35 to 95 g L^-1 or 35 to 85 g L^-1, and survival was monitored from 0.5-3.5 h or 0.5-53 h, for P. maculatofasciatus and L. guttatus, respectively. The results showed that mortality increased differently among treatments from the first exposure time in each species. Extreme salinities were lethal in 30 min. Salinities close to the control were sub lethal. At intermediate salinities, mortality was fitted to a potential or linear model. For P. maculatofasciatus, the LC₅₀ values obtained between 0.5 and 3.5 h were 73.4 to 65.4 g L^-1. For L. guttatus the LC₅₀ values obtained between 2 and 5 h were 57.3 to 54.5 g L^-1. Comparison of LC₅₀ between species showed that P. maculatofasciatus larvae had a higher tolerance to hyperosmotic stress. Based on the results for each species, it is recommended to expose to 70 g L^-1 for 1 h for P. maculatofasciatus and 57 g L^-1 for 2 h for L. guttatus when conducting hyperosmotic stress tests. This stress test is objective, simple, and can be used in both studies on broodstock nutrition and management and in hatcheries as a quality control method.