Effects of toxic dinoflagellate Alexandrium catenella on sexual maturation and reproductive output in the pacific oyster Crassostrea gigas.

Marine bivalves which feed mainly on microalgae could accumulate toxins during harmful algal blooms, posing a health hazard to humans and other animals through food chains. The Pacific oyster (Crassostrea gigas) is the globally dominant farmed bivalves in the world. In order to benefit sustainable development of the oyster aquaculture, we assessed the effects of an artificial bloom of the toxin-producing dinoflagellate, Alexandrium catenella, upon sexual maturation in C. gigas. Oysters were exposed to A. catenella from April to June in 2012, and compared to a control batch of oysters fed with Isochrysis galbana. During the exposure, clearance, histological observations, biochemical composition as well as embryonic development were measured. The results indicated that A. catenella could be a food source, and inhibited the clearance rate of C. gigas for I. galbana. Significant pathological changes in the form of degeneration in adductor muscles, mantle, ovary and tubules and several inflammatory responses were observed in C. gigas when exposed to harmful microalga. The exposure of A. catenella had negative effects on assimilation, biochemical composition and so as the reproduction. The results of this study demonstrated that toxic microalga can affect "quality'' of eggs and the consequences, in terms of fertility, embryo and larval output.