Efeito da adição de Navicula sp. e Brachionus plicatilis na taxa de infecção de Litopenaeus vannamei desafiados com o Vírus da Síndrome da Mancha Branca (WSSV) na fase berçário e cultivados em sistema intensivo

Abstract

Currently in shrimp farming, intensive system is a promising technique because it has greater biosecurity in relation to traditional culture, especially regarding the challenges with the White Spot Syndrome Virus (WSSV). The aim of this study was to evaluate the effect of the combined and isolated addition of Navicula sp. and Brachionus plicatilis on zootechnical performance, water quality, Vibrio concentration and WSSV infection of L. vannamei reared in nursery with biofloc system. The study was divided into two phases, the first phase consisting of four treatments: BFT (biofloc); BFT-N (BFT with the addition of Navicula sp.); BFT-B (BFT with the addition of Brachionus plicatilis) and; BFT-BN (BFT with the addition of Navicula sp. and Brachionus plicatilis), all in triplicate and; the second phase, it was constituted by viral challenge, also in triplicate. Shrimp (PL10, 2 mg) were randomly separated and distributed in the experimental tanks at 3000 shrimp m-³ and fed four times a day with a 45% protein commercial shrimp diet. Live food was added every 10 days at a density of 10x104 cel mL-1 for Navicula sp. and 30 org mL-1 for Brachionus plicatilis. After 45 days of experiment, the animals were infected with WSSV using minced tissue (21 days) at density of 300 cam m-³. Results indicate that for the first phase, final weight and yield were statistically significant for all treatments with isolated and combined addition of diatoms and rotifers. In this phase, there was a predominance of positive sucrose colonies in Vibrio quantification. Massive mortality rate was firstly achieved in control (BFT) and BFT-B treatments in the second phase. However, all treatments achieved 100% of mortality rate and the WSSV infection was confirmed by nested-PCR and histopathologically, with lesions suggestive of WSD (presence of nodules and tissue deformations). Although the addition of live food resulted in best zootechnical indexes of L. vannamei in intensive nursery system, in terms of resistance to WSSV infection, there was no reduction in infection and mortality rates in challenged animals under the experimental conditions examined.