ABSTRACT Microbiota, the microorganisms that colonize living organisms. Oysters rely exclusively on an innate immune system. This study characterized the cultivable gastrointestinal tract microbiota (GTM) of the oyster Crassostrea gasar and evaluated their influence on immune responses. Antibiotics were used to reduce or alter the microbiota during in vitro and in vivo assays. Haemocyte viability, concentration, and phagocytic capacity, as well as the production of reactive oxygen species (ROS), were evaluated in antibiotic-treated and control oysters. Microbiological analysis of the gastrointestinal tract was also performed; bacteria were selected using culture media and were identified by 16S ribosomal DNA. The results showed that the antibiotics eliminated bacteria in vitro but increased their concentrations in vivo. The GTM was composed of 26% amylolytic bacteria, 21% lipolytic bacteria, 18% proteolytic bacteria, 18% cellulolytic bacteria and 17% lactic acid bacteria; there were no differences in the amounts of these bacterial types between the control and treated oysters. Three major bacterial phyla, Proteobacteria, Firmicutes and Actinobacteria, and seven genera, Labrenzia, Pseudomonas, Halomonas, Shewanella, Vibrio, Bacillus, and Micrococcus, were detected. The concentration, viability, and phagocytic capacity of hemocytes and the production of ROS were not significantly altered by antibiotic treatment. In conclusion, the antibiotics altered the number of heterotrophic bacteria without changing hemocyte function, suggesting that this assay could be useful for verifying the influence of microbiota in host-parasite interactions.

Resumo Crassostrea rhizophorae e C. gasar são cultivadas na região Nordeste. Parasitas Perkinsus infectam bivalves e seus efeitos em ostras de regiões tropicais são pouco compreendidos. Este estudo avaliou o impacto da infecção por Perkinsus em parâmetros de produção de ostras nativas. Ostras foram coletadas bimestralmente durante 7 meses, de julho de 2010 a fevereiro de 2011, para avaliar crescimento, mortalidade e padrão de coloração da concha (branca e cinza-escura) (n = 500); além da presença e intensidade de Perkinsus (n = 152). Perkinsus e Crassostrea foram identificados por abordagem molecular. Os resultados mostraram que as ostras cinza-escuras (90%, n = 20) e brancas (67%, n = 18) eram C. gasar e C. rhizophorae, respectivamente. As ostras mostraram uma boa taxa de crescimento e mortalidade acumulada moderada (44%). C. gasar cresceu melhor com menor mortalidade e menor incidência de Perkinsus que C. rhizophorae. A prevalência média de Perkinsus foi moderada (48%), mas a intensidade de infecção foi leve (2,2). A perkinsiose afetou ostras pequenas (19,4 mm). Em conclusão, ostras nativas, especialmente C. gasar, têm grande potencial de produção; sem mortalidade associada à perkinsiose; e, a cor da concha pode ser usada para melhorar a seleção de sementes com melhor desempenho.

Abstract Crassostrea rhizophorae and C. gasar oysters are cultivated in the northeast region. Perkinsus parasites infect bivalves, and their effects on oysters from tropical regions are poorly understood. This study evaluated the impact of Perkinsus infection on the productive traits of native oysters. Oysters were sampled bimonthly during 7 months, from July 2010 to February 2011, to evaluate growth rate, mortality and shell color patterns (white and dark-gray) (n = 500), and to determine the prevalence and intensity of Perkinsus (n = 152). Perkinsus and Crassostrea species were determined using molecular tools. Results showed that most dark-gray (90%, n = 20) and white (67%, n = 18) oysters were C. gasar and C. rhizophorae, respectively. Oysters showed a high growth rate and moderate cumulative mortality (44%). C. gasar oysters grew better and showed lower mortality and lower incidence of Perkinsus compared to C. rhizophorae. The mean prevalence of Perkinsus was moderate (48%), but the infection intensity was light (2.2). Perkinsosis affected very small oysters (19.4 mm). In conclusion, native oysters, especially C. gasar, have a great potential for culture, mortality is not associated with perkinsosis, and the shell color of oysters can be used to improve selection for spats with better performance.

Resumo O cultivo de bivalves é de grande interesse econômico e social no Nordeste (NE) do Brasil. O policultivo é uma alternativa ao monocultivo tradicional de camarões para reduzir o impacto ambiental e melhorar a produção de ostras.Perkinsus marinus e Perkinsus olseni foram identificados infectando ostras no Nordeste do Brasil e representam uma ameaça a produção de ostras. Este estudo avaliou a ocorrência dePerkinsus spp. em Crassostrea gasardurante todas as fases de produção. Sementes de ostras foram produzidas em laboratório e cultivadas em viveiros de camarão no Rio Grande do Norte.Perkinsus spp. foram diagnosticados com o uso do meio de tioglicolato fluido de Ray e confirmado por reação em cadeia da polimerase. A prevalência e intensidade de infecção foram determinadas em ostras até atingirem 7 cm. Os resultados mostraram que os reprodutores encontravam-se infectados porPerkinsus (60%), mas as sementes produzidas estavam livres de Perkinsus. As sementes adquiriram a infecção porPerkinsus quando transferidas para os viveiros. A prevalência aumentou gradualmente nos sete meses após a colocação nos viveiros (73%) e, em seguida, diminuiu para 17% até o décimo mês. As infecções foram inicialmente leves, mas aumentaram até a fase final do crescimento. Em conclusão, é possível produzir sementes de ostras C. gasarlivres de Perkinsus a partir de reprodutores infectados e seu cultivo em viveiros de camarão é viável.

Abstract Bivalve culture is of considerable economic and social interest in northeastern (NE) Brazil. The polyculture is an alternative approach to traditional monoculture for reducing the environmental impact of shrimp farming and improving oyster culture. Perkinsus marinus andPerkinsus olseni were found infecting oysters in NE Brazil and can threaten oyster production. This study evaluatedPerkinsus spp. occurrence in Crassostrea gasar during all production stages. Oyster spats were produced in a hatchery and grown in shrimp ponds in Rio Grande do Norte state.Perkinsus spp. were surveyed by Ray’s fluid thioglycollate medium and confirmed by polymerase chain reaction. Prevalence and intensity of infection were determined in oysters until they reached 7 cm. Results showed that the broodstock was already infected by Perkinsus (60%), but the derived spats were Perkinsus-free. Oyster spats acquired Perkinsus infection when transferred to ponds. The prevalence gradually increased in the seven months following placement in ponds (73%), and then decreased to 17% by the tenth month. The infections were initially mild, but intensity increased at the final growth stage. In conclusion, it is possible to produce Perkinsus-free C. gasar oyster spats from infected broodstock, and their culture in shrimp ponds is feasible.