Composition, density and biomass of zooplankton in culture ponds of Litopenaeus vannamei (DECAPODA: PENAEIDAE) in southern Brazil.

Litopenaeus vannamei is the most cultivated shrimp species in Brazil, being fed basically on high protein formulated diets. However, some studies have shown that the natural zooplankton found in shrimp ponds can be part of the diet of this crustacean. In this study, the zooplankton composition, density and biomass were evaluated for two shrimp ponds from a shrimp farm in the Patos Lagoon estuary, in southern Brazil (32°00’S, 51°59’W) between 11/09/2005 and 01/20/2006. The two ponds were sampled over three consecutive months using a zooplankton net of 150 cm total length, 30 cm mouth diameter and 140 µm nylon mesh size. All the zooplankton samples were preserved in formaldehyde solution at a final concentration of 4% and transported to the laboratory, where the composition, density and biomass (wet and dry weight) were assessed. Copepoda and Cladocera were the most frequent groups, while the most abundant species were Acartia tonsa, Pseudodiaptomus richardi and Moina micrura,species commonly found in the Patos Lagoon Estuary. The density values obtained in the ponds were higher than those usually found in the estuary during periods of maximum production, reaching 278 org.L-1 in 11/18/2005 (pond 1), and 277 org.L-1 in 12/08/2005 (pond 2), suggesting that the zooplankton grow well in the shrimp ponds. Zooplankton biomass in the ponds was also relatively high, ranging from 0.15 to 13.28 g.m-3 of wet weight and 0.01 to 2.72 g.m-3 of dry weight, following the same tendency of density. These results clearly indicate that the natural zooplankton occurring in the shrimp ponds represents a potential food source for the shrimp larvae and juveniles during the first months of culture.