Avaliação do impacto das microalgas tóxicas Prorocentrum lima e Ostreopsis cf. ovata sobre as respostas de defesa e fisiologia da ostra Crassostrea gasar

Abstract

The present work aimed to evaluate the effect of harmful microalgae Prorocentrum lima and Ostreopsis cf. ovata in the immune responses of the oyster Crassostrea gasar. For this purpose, hemocytes were exposed (in vitro) to P. lima and O. cf. ovata and oysters were exposed (in vivo) to O. cf. ovata, histopathological analysis and diagnosis of Perkinsus spp.. Cytograms, mortality, total (THC) and differential (DHC) hemocyte count, phagocytic activity, production of reactive oxygen species (ROS) and activity of ABC hemocyte transporters were determined by flow cytometry. Histological sections were prepared. The detection of Perkinsus spp. and its intensity was determined in the demibranchs. The results of this study showed that O. cf. ovata is potentially more toxic to hemocytes than P. lima. In the in vitro exposure, O. cf. ovata increased the mortality of hemocytes in the highest concentrations, 81.2 ± 1.51% (Fórmula) and 86.9 ±

1.50% (Fórmula), reduced the rate of phagocytosis to O. cf. ovata (up to 2x) and the production of ROS was not affected, as well as the activity of ABC transporters. In in vivo exposure, THC, the percentage of hemocyte subpopulations, the rate of phagocytosis and the activity of ABC transporters did not change. However, hemocyte mortality doubled in the treated group and ROS production decreased in the treated oysters hemocytes, blast cells (3.8x) and hyalinocytes (3.4x) showed a similar reduction, and greater than granulocytes (2.3x). Histopathological analysis revealed that the digestive gland is the organ affected by O. cf. ovata. Perkinsus spp. proliferation was observed in the tissues of treated oysters favored by O. cf. ovata. Although animal mortality has not been observed, impaired hemocytes suggest an immunosuppression that can lead to opportunistic infections or increase the damage caused by pathogens already present.