Influência do farelo de trigo na disponibilidade do alimento natural e no crescimento do camarão Litopenaeus vannamei (Boone, 1931)

Abstract

The shrimp Litopenaeus vannamei adapted itself very well to the culture conditions in the Northeast due to their characteristics of tolerance to the salinity and temperature, resistance to the handling, rapid growth and survival and good feed conversion, contributing to place Brazil in the producer and exporter market. Even with the good productivity results, there are some limiting factors to be better studied, as the feeding, where the production and the adequate management of the natural food contributing to improve the economical and environmental feasibility of the culture and represents great nutritional importance to the cultivated organisms. The aim of this study was to analyze the influence of organic fertilizer in the availability of natural food (plankton and benthos) and the shrimp growth, with the purpose of effluents and costs reduction, through two fertilization regimes in four treatments: 1) CP: Control (inorganic fertilizers) stocked with 40 juveniles.m-2; 2) CNP: Control no-shrimp; 3) TP: Wheat bran (organic fertilizer) stocked with 40 juveniles.m-2; 4) TNP: Wheat bran no-shrimp, with three replicates each. The experimental tanks were prepared with sediment, individual aeration, without water exchange, and the shrimps feeding during 88 culture days, was done with a commercial 35% crude protein ration through feeding trays, three times a day, adjusted daily to the according consumption. The water temperature, dissolved oxygen and pH were measured daily; the transparency and salinity were checked weekly and samples of water of each tank were collected biweekly for nutrients analyses. The phytoplankton analysis, zooplankton, phytobenthos and meiobenthos samples were accomplished biweekly and macroinvertebrates samples were monthly. The dissolved oxygen levels were higher with the wheat bran (6.16±0.98 mg.L-1) than with the inorganic fertilizers (5.92±1.19 mg.L-1). Under organic fertilization regime, the phytoplankton presented abundance of Bacillariophyceae, mainly Nitzschia, and rotifers; the phytobenthos was constituted of Bacillariophyceae, mainly for Nitzschia, Amphiprora and Cymbella; the meiobenthos mainly for nematodes and rotifers; and the macroinvertebrates were constituted mainly of oligochaetas. The feeding preference of the shrimps was decisive in the abundance of natural food, which determined different conversion ration along the experiment (1.3 and 2.1), justifying periodic adjustments of the amount of artificial diets. The shrimps survival was the same for both fertilization regimes (96.6%). The final weight in CP was of 11.89±1.73 g and in TP was of 12.28±1.71 g, with lower cost of the wheat bran in relation to the inorganic fertilizers. The wheat bran showed better performance not only in the water quality maintenance without exchange but also in the availability of natural food, and the performance of the shrimps, contributing to the minimize shrimp culture effluents and its impact on the environment, also in the reduction of the production costs.