Produtividade Primária do Biofilme em Cultivos dos Camarões Marinhos Farfantepenaeus paulensis e Litopenaeus vannamei.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The primary production of biolm, or periphyton (a microorganisms community attached to submerged natural or artificial substrates) has been used for a long time as a strategy to improve the water quality and as a complementary food source for raised organisms. In spite of the importance of natural productivity in aquaculture systems less atention is given to direct measurements of periphyton primary production rates in cultivation systems, specially in shrimp farming. Therefore, we aimed in this study to evaluate the periphyton primary production levels in shrimp culture systems of Litopenaeus vannamei and Farfantepenaeus paulensis, as well as to determine the effects of abiotic factors and shrimp predation on the periphyton microalgae. Two experiments were carried out with each species during 38 days in November 2006 and April 2007, at the Aquaculture Marine Station - EMA/FURG. In each experiment, three treatments containing artificial substrates (nylon nets with 1 mm mesh size) in 150 L plastic tanks were arranged in the following way: 1) Treatment CR, with shrimp and ration addition; 2) Treatment R, only with ration addition and 3) Treatment Control, containing only the substrates. During this period periphyton samples were collected for primary production measurements, analysis of Chlorophyll a, dry weight and abundance of microorganisms. The experiment with L. vannamei was characterized by high water temperatures and salinities, which were positively correlated with the primary production levels. These shrimps grazed effectively on nematodes and diatoms (Cymbella less than 20 μm) forcing a substitution of dominant diatom by r-strategists species. Such succession probably promoted the high primary production rates in the CR treatment (0.0022 to 0.117 mgO2 cm−2.h−1), in comparison to other treatments. The chlorophyll a varied between 0,52 and 1,8 μg cm−2. In the F. paulensis experiment, higher microalgae biomass occurred at CR treatment, with chlorophyll a values between 0.19 and 8.25 μg cm−2. The lower primary production 10 rates in this treatment (0.0015 to 0.050 mgO2 cm−2.h−1) was possibly caused by shading of the microalgae due to the several layers of periphyton. This shrimp consumed mainly larger diatoms and nematodes. Knowing the net production of the systems and the metabolic rates (respiration) of L. vannamei and F. paulensis it was possible to calculate how much of the shrimps metabolic necessity could be supplied by the periphyton primary production. In the case of L. vannamei, net production of the whole system might provide 8 to 150 % of this shrimp demands, whereas for F. paulensis, which has a smaller metabolic activity, the primary production of the periphyton in the tanks might provide 137,63 to 287,78 % of the shrimp metabolic necessity. The results of this work demonstrate that biofilm primary productivity can provide great fraction of the shrimp nutritional demand. The periphyton growth in shrimp culture systems can represent an increase in the availability of foods for the shrimps, which might represent an important reduction of costs, since feeding represents more than 50 % of the total of production costs.

ASSUNTO(S)

produção primária litopenaeus vannamei biofilme aquicultura farfantepenaeus paulensis perifiton

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