Browsing by Author "Brink, Jacobus Abraham"

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    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
    (Stellenbosch : Stellenbosch University, 2006-04) Brink, Jacobus Abraham; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Reports of a wonnlike "parasitic" infestation of pacific oysters, Crassostrea gi.gas combined with an increased mortality on a land based oyster farm on the west coast of South Africa prompted an investigation as to the identity of the infesting organisms, the extent of the infestation and the impact on the condition of the oysters. As the infesting organism was suspected to be a member of the polydorid complex of the spionid polychaeta, a literature study was conducted and the information gathered, compiled in the form of a review which also serves the 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 the group. The infesting organism was identified as a member of the spionid polychaeta and specifically the genus Polydora, a known pest in bivalve molluscs. It was found that the organism showed varied levels of infestation in the spatially and age segregated oyster population on the farm with the oldest animals the heaviest infected and also the possible source of the infestation as they were brought onto the farm from another oyster farm. The condition of all the animals in the different cohorts 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 infested and uninfested oysters and therefore it cannot be conclusively proved that the increased mortalities can be ascribed to the polydorid infestation. Although no single cause seemed to be implicated the mortalitie can probably ascribed to a combination of several extrinsic and intrinsic factors. The implementation of quality control systems such as HACCP on aquaculture farms is critical for successful cultivation. A set of Best Management Practices (bmp) for the culture of bivalve molluscs is proposed, with identification and special reference to the critical control points as required by HACCP. The current practices on the farm in question were also investigated and it was concluded that the absolute lack of management on the farm was the primary cause for the · problems experienced.