Polydorid polychaeta as pests in cultivated oysters : a case study of polydorid infestation on a South African oyster farm, including a literature review and proposed best management practices for the reduction of polychaete infestation in the culture of molluscs

[摘要] ENGLISH ABSTRACT: Reports of a wonnlike parasitic infestation of pacific oysters, Crassostrea gi.gas combinedwith an increased mortality on a land based oyster farm on the west coast of South Africaprompted an investigation as to the identity of the infesting organisms, the extent of theinfestation and the impact on the condition of the oysters. As the infesting organism wassuspected to be a member of the polydorid complex of the spionid polychaeta, a literature studywas conducted and the information gathered, compiled in the form of a review which also servesthe purpose of a practical guide for aquaculturists who have to deal with polydorid infestations.The review summarizes information on the systematics, life history, impact and control of thegroup.The infesting organism was identified as a member of the spionid polychaeta and specifically thegenus Polydora, a known pest in bivalve molluscs. It was found that the organism showed variedlevels of infestation in the spatially and age segregated oyster population on the farm with theoldest animals the heaviest infected and also the possible source of the infestation as they werebrought onto the farm from another oyster farm. The condition of all the animals in the differentcohorts on the farm was good compared to international standards (condition indexes (Cl)> 10)ANOV A analysis of data could find no significant difference between the condition of infestedand uninfested oysters and therefore it cannot be conclusively proved that the increasedmortalities can be ascribed to the polydorid infestation. Although no single cause seemed to beimplicated the mortalitie can probably ascribed to a combination of several extrinsic andintrinsic factors.The implementation of quality control systems such as HACCP on aquaculture farms is criticalfor successful cultivation. A set of Best Management Practices (bmp) for the culture of bivalvemolluscs is proposed, with identification and special reference to the critical control points asrequired by HACCP. The current practices on the farm in question were also investigated and itwas concluded that the absolute lack of management on the farm was the primary cause for the· problems experienced.

[发布机构] Stellenbosch University