Shift in functional and morphological parameters of the Pacific oyster hemocytes after exposure to hypoxia

Abstract

Bivalve mollusks are widely spread in shallow areas where they are subjected to fluctuations of dissolved oxygen concentration. The rapidly occurring hypoxia can represent a significant impact on bivalve immunity and functional status of the organism. The Pacific oyster (Crassostrea gigas) is an intensively cultivated introduced species in the Black Sea, which is poorly studied as a region for aquaculture. In this work the effect of 72 h hypoxia (2.1 mg O2L−1) on hemocyte functional parameters as well as immune markers of C. gigas were investigated. Hemolymph cellular composition, hemocyte proliferation level, mortality, and mitochondrial membrane potential, phagocytic capacity and spontaneous reactive oxygen species (ROS) production were evaluated using flow cytometry and microscopy. Exposure to hypoxia significantly affected hemolymph cellular composition by increasing the number of agranulocytes. Granulocyte and hyalinocyte number did not change. After 72 h exposure period changes in hemocyte morphology and massive cell aggregation were observed on slides. Cellular and nuclear diameter of agranulocytes decreased upon exposure to hypoxia The non-stimulated production of ROS significantly decreased in all hemocyte types. Phagocytic activity, hemocyte proliferation and mortality level were not significantly influenced by oxygen deficiency. The results of the present work indicate a pronounced negative impact of 72 h hypoxia on physiological parameters of hemocytes, which, however, was not associated with a decrease of their immune capacity.