Microbial flocs: zootechnical aspects of the cultivation of the pink shrimp Farfantepenaeus paulensis and Farfantepenaeus brasiliensis
The relevance of this study was to assess the potential of microbial flakes compared to conventional "clear water" crops in the growth and survival of post-larvae of Farfantepenaeus paulensis and Farfantepenaeus brasiliensis. F. paulensis post-larvae (experiment 1) were grown in the pre-nursery phase for 15 days at a density of 10PL / L. In experiment 2 and 3, for 30 days, post-larvae (PL25) of F. paulensis and F. brasiliensis were grown at a density of 500PL / m2, in the following treatments: cultivation in the presence of microbial flake with feed supply: ( FLOC + R); cultivation in the presence of the flake without feed: (FLOC); cultivation in clear water with feed supply: (AC + R) and cultivation in clear water without feed supply: (AC) (the latter only in the work done with F.brasiliensis), each experimental unit consisting of a rectangular plastic box with a useful unit volume of 40 liters (experiment 1 and 2) and network tanks (experiment 2) - both called microcosms, where the boxes were provided with aeration through porous stones and a total daily recirculation rate of approximately 150% / day. For such recirculation, the water was pumped from a 7000 L matrix tank where intensive cultivation of shrimp occurred in heterotrophic medium and zero exchange by means of a submerged pump and returned by gravity. In the study with F. brasiliensis, the network tanks were allocated directly inside the matrix tank for treatments in the midst of microbial flakes. In “clear water” cultivation, a fiber cement reservoir with a useful volume of 800 liters (renewed 100% daily) was used,following the same recirculation and pumping scheme described above or allocated directly to it (experiment 3). The formation of microbial aggregates respected the following stages: population of the “matrix tank” with juvenile shrimp ( 5g), inoculation of the diatom Thalassiosira weissflogii and organic fertilization respecting the nominal C / N ratio (by weight) of 30: 1, balanced according to the chemical composition of each ingredient (wheat bran, sugar cane molasses and the feed provided to the animals). The results showed that in experiment 1 the treatment in the midst of microbial flakes with feed supply, the post-larvae obtained at the end of the experiment greater final weight, weight gain (15 days) and final length, compared 9 to the other treatments (P <0.05). Regarding survival,the treatment with and without feed supply in the flakes did not differ among themselves (P> 0.05), but they were superior to the treatment in clear water with feed supply (P <0.05). In experiment 2, the treatments in the presence of microbial flakes with feed supply and in clear water with feed supply did not differ (P> 0.05), in relation to the final weight, weight gain (30 days), final length and survival. However, both showed superior results (P <0.05) when compared to the treatment where the animals were grown in heterotrophic medium without the supply of feed. In experiment 3, in relation to the final weight, the animals grown in the middle of the flakes with and without feed supply did not differ from each other (P> 0.05),however, presenting final weight and weight gain (30 days) higher (P <0.05) than animals grown without the presence of aggregate. However, there were no effects of treatments on survival and final total length, except in the AC treatment where the animals were smaller (P <0.05). Thus, in general, the presence of microbial flakes contributed to a better growth and survival of the shrimp. This fact can be attributed to a huge range of microorganisms present in the environment, this being a rich source of essential amino acids, vitamins, animal ability to capture the material, among others, besides canceling the emission of effluents in adjacent environments, contributing to a culture more rational.