Influência do sistema de cultivo no desempenho zootécnico e resposta à infecção pelo Vírus da Síndrome da Mancha Branca em pós-larvas de camarão marinho Litopenaeus vannamei (Boone, 1931)

Abstract

Aquaculture is currently one of the main means of obtaining food of aquatic origin in the world and its global production corresponds to 47% of the world production of aquatic organisms, equivalent to more than 80 million tons. Of the groups produced, the production of crustaceans stood out, which in 2016 was 7.9 million tons, with the marine shrimp, Litopenaeus vannamei, accounting for 65.3% of this total. However, this production has been constantly threatened by disease outbreaks, requiring a productive approach that applies biosecurity measures, adequate nutrition, promoting the immunity of cultivated animals and maintaining good water quality, to maintain homeostasis, which translates into if in the biofloc system (BFT). However, although L. vannamei kept in this system has achieved better zootechnical rates when compared to traditional systems, little is known about the influence of the transfer of animals to different cultivation systems, during the nursery phase, on zootechnical performance and immune resistance to White Spot Syndrome Virus – WSSV. Therefore, the objective of the present study was to evaluate the influence of Litopenaeus vannamei exposure, during the nursery phase, and the alteration of the culture system, on zootechnical performance and immunological resistance to WSSV. Two systems were evaluated, Biofloc - BFT and Clear Water Recirculation - CW, in three steps: the first step, where the 10-day post-larvae (PL10’s - 290PL/g), were maintained for a period of 10 days in the respective systems; second step, lasting 30 days, which consisted, at the end of the 1st stage, in the redistribution of the Pl20’s for both systems, thus obtaining four treatments (BFT-BFT, BFT-CW, CW-BFT, and CW-CW) and the third step corresponding to the viral challenge. In these steps, it was determined: zootechnical performance variables; hematological variables (total and differential hemocyte counts); presumptive total count of Vibrio sp.; lesions suggestive of WSSV infection via histology and; infection and survival rate after viral challenge. The BFT system in terms of zootechnical performance, in general, proved to be efficient, especially in the early stages of the animal's life, with better results when compared to RAC. The results of the presumptive count of Vibrio sp. demonstrated growth in treatments originating from or maintained in BFT. Concerning the immune response and the influence of systems, hemato-immunological parameters were not influenced, however, it was observed that in a scenario of infection by WSSV, there was interference in the animal's immune response, resulting in a decrease in the amount of immunocompetent cells. Also, between treatments, there was a difference in the form of manifestation of the disease, as evidenced by histological analysis due to the higher concentration of suggestive lesions recorded in animals originating or maintained in BFT. However, despite the differences in the lesions found, all challenged animals were positive for WSSV via nested-PCR. Therefore, it was concluded that although BFT is considered a biosafety environment for cultivated animals, as it is a minimal or no water exchange system, in a WSSV infection scenario, it can induce a state of fatigue in the defense systems of cultivated animals due to the continuous stimulation of the immune system due to the microorganisms contained in the flakes, which may lead the animals to a condition of greater vulnerability. And although a scenario of co-infection with WSSV and Vibrio sp has not been evaluated, the possibility of its occurrence would result in the potentiation of the WSSV infection, especially in the system with BFT, considering the high vibrionaceaes concentrations accounted for.