A mortality event of the venerid bivalve Callista chione (Linnaeus, 1758) in a hatchery system- A case study.

Abnormal mortality of the smooth venus clam (Callista chione) was encountered when conditioning these clams in a hatchery system. A histopathological analysis was performed to establish the causes of this mortality episode. Our results showed an increase in rickettsia-like bacteria infection intensity between the individuals collected at the start of the conditioning in the hatchery and those collected during the mortality episode. Husbandry stress most likely increased disease susceptibility and progression in these clams. Rickettsia-like colonies were observed in large number in the gills of all individuals examined. Nematopsis sp. spores and rod-shaped basophilic bacteria could also been seen in some of the individuals examined. Microbiological analysis of tissue clam did not reveal the presence of any potentially pathogenic bacteria and all the clams were shown to be free of Perkinsus sp. parasites. The conditioning protocol was adapted from those used for other venerid clam due to the lack of data on this species. This study highlights the need to perform further studies to evaluate the optimal parameters for C. chione broodstock conditioning.