Administration of sulfated polysaccharides as immunostimulant agents can reduce the stress impact in aquatic organism’s culture during shrimp and fish larvicultures. The aim of this work was to evaluate the effect of immersion baths containing different concentrations of sulfated polysaccharides (SP) extracted from the marine red alga Botryocladia occidentalis on Litopenaeus vannamei shrimp post-larvae (PL20) survival rate and weight growth. The tested doses were administrated in four treatments with four repetitions. The treatments were with 0.5; 1.0 and 1.5 µg.L-1 SP, respectively, and the control without polysaccharides. The experiment lasted eight days and within this period three immersion baths were done with a 24 hours rest interruption among each bath. Treatments presented weight gains changing from 23; 37 to 28, 30 mg and were not significantly different (P < 0.05). Treatments 0 (control), 0.5; 1.0 and 1.5 µg.L-1 post-larvae survival rates were 30.63 ± 5.56; 36.10 ± 5.71; 26.20 ± 4.00 e 23.50 ± 5.59 mg, (Average ± SD) respectively, and 1.0 µg.L-1 SP treatment survival rate was significantly different from the treatment 0 (control) and 1.5 µg.L-1 SP treatments. These results showed that a 1.0 µg.L-1 dose of SP enhance L. vannamei shrimp
