Effect of diet on the quality of post-larvae of White Shrimp Litopenaeus vannamei produced in biofloc systems (Boone, 1931)
This Thesis aimed to determine the influence of bioflocs (microbial flakes) and different food sources on the development of post-larvae of the white shrimp Litopenaeus vannamei between the phases of PL1 and PL30, through larval quality indicators, histological techniques for the assessment of hepatopancreas and the δ13C and δ15N stable isotope technique. This Thesis is structured in the form of a general introduction, with a bibliographic survey on the early life stages of peneid shrimp, as well as criteria for verification of food consumption and evaluation of post-larval quality and its possible methods of analysis and four chapters, in addition to general discussion and final conclusions. In chapter I, two experiments were carried out with post-larvae of Litopenaeus vannamei,the first experiment tested post-larvae between the phases of PL1 and PL15 and the second experiment post-larvae between the phases of PL16 and PL30, both with two treatments (bioflocs vs. clear water), compared using histological techniques to assess the hepatopancreas and previously selected quality criteria. The results of this chapter demonstrated that the production of post-larvae in the midst of bioflocuses results in organisms with better final quality and better development of the hepatopancreas and with a greater presence of digestive cells, when compared to those grown in clear water. Chapter II characterizes the microbial community of the tested treatments (bioflocs vs. clear water) and uses the technique of stable isotopes of δ13C and δ15N, to determine the influence of bioflocs, of different types of feed, of Artemia sp.and microalgae Chaetoceros muelleri in the growth of post-larvae. These results allowed us to observe that, at the end of the experimental period, bioflocs are made up mainly of protozoa and microalgae, and in the biofloc system, microalgae are maintained without the need for inoculations after the tenth day, continuing to contribute as a food source, since although post-larvae mostly assimilate nursery-specific feed, they are able to consume and incorporate bioflocs into their tissues. In chapters III and IV, the stable isotope technique and the histological analysis of the hepatopancreas were used as tools to analyze the contribution of different food sources to the growth and nutritional status of Litopenaeus vannamei post-larvae,the experiment in chapter IV being developed in the middle of bioflocs and without water renewal and the experiment presented in chapter V developed in the middle of clear water with water renewal. The food sources provided were Chaetoceros muelleri, Artemia sp. and specific commercial feed for shrimp nursery. In the course of both experiments, the colonization of the tank walls by a biofilm was detected, which was considered as a food source. In the experiment in Chapter III, it was found that commercial feed contributed to a greater portion of the growth of L. vannamei post-larvae, however a substantial contribution of bioflocs to the growth of animals was observed. Biofilm also contributed as a food source and, together with biofloc, contributed to maintaining water quality.According to the results of the analysis of the hepatopancreas and stable isotopes, it can be concluded that bioflocs and microalgae C. muelleri can be used instead of Artemia sp., Since both sources provide for the production of organisms with good characteristics histological findings of the hepatopancreas, in addition to not needing successive inoculations over time. In the experiment in chapter IV, it was verified that there was assimilation of the biofilm by the post-larvae, however, its assimilation was not effective to improve performance and ensure water quality. Artemia sp. it was presented as the most effective source of live food for the nutritional quality of post-larvae and its supply should not be replaced by C. muelleri during the nursery phase in the midst of clear water.Based on the results of this thesis, it can be concluded that the suspension of water renewals does not generate losses for the production of post-larvae of Litopenaeus vannamei, with the possibility of starting production in biofloc systems since the PL1 phase. In this type of system, post-larvae consume and incorporate bioflocs into their tissues, in addition to presenting a better quality standard than those produced in traditional systems. In biofloc systems the supply of Artemia sp. as a food source it can be successfully replaced by the microalgae C. muelleri.