Efeito de densidades de estocagem na disponibilidade de alimento natural em berçário de camarão Litopenaeus vannamei (Boone, 1931) cultivado com tecnologia de biofloco

Abstract

The objective of this work was to determine the main components of planktonic food in the nursery of shrimp L. vannameiwith biofloc technology. The experiment was carried out for 28 days and a randomized design with three post-larval storage densities, D2: 2 PLs. L-1, D4: 4 PLs. L-1and D6: 6 PLs.L-1, with four replicates each, using molasses as carbon source, in the C: N ratio of 15: 1. Samples were collected weekly, with 2 liters of water in each tank, which were filtered with plankton net and concentrated in 250 mL. The qualitative and quantitative study of plankton with 1 mL sub-samples for zooplankton was carried out in the Sedgwick-Rafter chamber (ind.L-1). The phytoplankton was evaluated in slides and coverslips (nº cells.mL-1) analyzing 0,1 mL, bothunder light microscope. The temperature values remained close to 22 ° C, below the ideal temperature for L. vannameicultivation, since the appropriate range for this species is between 26 to 33ºC, but the dissolved oxygen was in the ideal conditions for its culture, which should be above 4.0 mg.L-1and during the experiment remained above 8 mg.L-1. The development of shrimp did not show any difference between the treatments, for the final weight variable, since the survival, the D2treatment obtained the highest survival (> 72%) and the production in D6was higher than in the other treatments (2.98 Pls.L-1). The zooplankton community in the nursery tanks was represented by 23 genera, distributed among the groups Rotifera, Protozoa, Nematoda, Platelmintos and Cladocera. The Protozoa group presented the most diversification, regardless of the treatment, and also presented the highest abundance (> 66%). The main genera of Protozoa were Aspidisca, Euplotesand Trinema, and the phytoplankton community was composed of 16 genera, distributed in the classes Chlorophyceae, Bacillariophyta, Cyanophyceaeand Dinophyceae, the dominant class was Bacillariophyta(> 41%), with the genera Naviculaand Cyclotella. The density of 4 PL.L-1gave the highest density of zooplankton, but for the phytoplankton the density of 6 PLs.L-1was the one with the highest amount.