Use of different carbon sources in the cultivation of Litopenaeus vannamei shrimp in a biofloc system
The technology of the biofloc cultivation system (BFT) allows the intensification of stocking density, as well as the increase in productivity, which requires management efforts to maintain water quality. However, one of the problems is the release of nitrogen through uneaten food, along with the excreta of the organisms grown, mainly in the form of total ammonia. The addition of organic carbon sources is an alternative in reducing ammonia making it possible to convert this compound into bacterial protein, being available as a supplementary food in the growing environment. Therefore, carbon sources such as sugarcane molasses, dextrose and rice bran were tested in the cultivation of L. vannamei shrimp in BFT systems,evaluating the reduction of the concentration of total ammoniacal nitrogen in experiments in the nursery and fattening phases, as well as the analysis of zootechnical performance of the animals. The experiments were carried out using boxes with a useful volume of 800 L. The nursery experiment lasted 35 days, with a stocking density of 1200 shrimp m-² and an average weight of 0.024 ± 0.01 g. The carbon sources of sugar cane molasses (M) and rice bran (F) were combined in different percentages. In the fattening experiment, stocking density of 300 shrimp m-², average weight of 4.09 ± 0.51 g, was used for 70 days. The treatments were distinguished by the sources of carbon dextrose and rice bran. In the nursery experiment, the concentration of ammonia was significantly lower (p <0.05) with the use of molasses.Nitrite accumulated until the end of the experiment, but due to the short experimental period it did not interfere in the zootechnical performance indexes, in which there were no differences due to the use of carbon sources. In the fattening experiment, with the use of dextrose, the ammonia concentration was significantly lower (p <0.05). Despite high concentrations of nitrite, the survivals were similar and above 80%. Zootechnical data such as final weight, weekly weight gain, apparent feed conversion and productivity were significantly better (p <0.05) in rice bran treatment. In both experiments, carbon sources of rapid degradation, such as molasses and dextrose were more efficient in reducing ammonia.The rapid degradation of these sources may have made available higher levels of carbon as a substrate for heterotrophic bacteria to metabolize ammonia, improving water quality.