Utilização das microalgas Thalassiosira weissflogii e Nannochloropsis oculata no cultivo de Litopenaeus vannamei em sistemas de berçários, sem renovação de água

The use of microalgae, Thalassiosira weissflogii (Diatom) and Nannochloropsis oculata (Eustigmatophyceae) in intensive nurseries with Litopenaeus vannamei, with zero water exchange, was evaluated in this study. Three treatments (control, Thalassiosira and Nannochloropsis) were conducted to observe the influence of microalgae on the parameters of water quality, microbiological, quality of larvae and their relationship with animal performance. The stocking density was 65 Pls/L. In addition to the microalgae, the post-larvae were fed with commercial diets high in protein (40-55%). The variables of water quality: temperature, oxygen, pH, salinity, alkalinity, concentrations of nitrite and nitrate, remained within the normal range for the species Litopenaeus vannamei. High levels of ammonia and phosphate were observed, but no influence on survival. The availability of nutrients favored the increase of pathogenic bacteria of the genus Vibrio. Survival, crude protein level in post- larvae, response to stress test, larval size and quality of post-larvae showed no significant differences. Differences were found in weight gain. Treatment with the microalgae Thalassiosira weissflogii exhibited the highest values of dry weight and consequently, greater weight gain and final biomass were observed.