First report of severe hemocytopenia and immunodepression in the sunray venus clam, Macrocallista nimbosa, a potential new aquaculture species in Florida

The Florida cultured hard clam industry has drastically increased over the past thirty years but is built upon a single species. In order to increase economic stability and growth of the industry, the sunray venus clam, Macrocallista nimbosa, is now being evaluated as a potential new aquaculture species. Very little is known about the physiological characteristics of this species. It is important to investigate the sunray venus clam's physiology, to predict its susceptibility to environmental variations, pathogens or pollutions. The objective of this study was to characterize the hemocytes in adult sunray venus clams, using flow cytometry. The present work led to the discovery of severe immunodepression in M. nimbosa from Florida. Immunodepressed individuals accounted for about 17% of clams and displayed a drastic loss of circulating hemocytes (hemocytopenia) as well as no immune capacity. Immunodepression was thought as resulting from a recent infection. Although immunodepressed individuals were not dying, severe immunosuppression may constitute a serious threat to the ability of sunray venus clams to cope with environmental or pathogenic stresses. Due to its current evaluation as a potential new aquaculture species in Florida, further investigations are necessary to determine the etiological agent and the impact on sunray venus clam populations.

► Sunray venus clam is a potential new aquaculture species in Florida.
► We characterized the hemocytes in this species.
► Severe hemocytopenia and immunodepression were discovered.
► Immunosuppression may represent a threat for sunray venus clam population.