The study evaluated the effect of oral administration of sulfated polysaccharides (SP) extracted from the marine macroalga Kappaphycus alvarezii on survival and weight gain of Nile tilapia post larvae during sex reversal in a stress situation. SP were extracted from the seaweed by enzymatic digestion and incorporated into the diet before the addition of the hormone 17-α-methyltestosterone, and administered at the doses of 0.05, 0.1 and 0.2 mg g-1 of body weight and a control (without SP), for 28 days. In the last week of sex reversal a stress situation was established by removing the aeration and water renewal. Survival and weight gains data were subjected to a variance analysis (ANOVA) and Tukey's test for averages differentiation at significance levels of 1 and 5%. Weight gains were greater in animals that received SP, regardless of the used dose and better survivals were obtained when SP were administered at the doses of 0.05 and 0.1 mg g-1, with values of 79.90 ± 5.68 and 77.60 ± 1.80%, respectively. The study revealed that small doses of the SP were able to improve survival, daily weight gain and final average weight of tilapias submitted to a stress situation.
seaweed; immunostimulant; sex reversal
