Paralytic shellfish poisoning in the abalone Haliotis midae on the West Coast of South Africa

摘要

In April 1999, monitoring on two West Coast abalone farms provided evidence of the presence of Paralytic Shellfish Poisoning (PSP) toxins in the cultured abalone Haliotis midae. Subsequent analysis of wild animals collected from the West Coast alsorevealed the accumulation of PSP toxins in these gastropods. The toxicity of individual animals as measured by the AOAC mouse bioassuy showed considerable variation, ranging from below the assay detection limit to a maximum of 1609 #mu#g STXeq 100 g~(-1). Initial observations found PSP toxins in abalone to be coincident with blooms of Alexandrium catenella indicating that this dinoflagellate was the probable cause of abalone toxicity. Subsequent detection by receptor binding assay, of toxicity in abalone on the South Coast, an area considered free of A. catenella blooms, casts some doubt as to the source of the toxins. The toxin composition in the abalone as determined by HPLC was dominated by STX, and differed significantly from the toxin profile of A. catenella and the co-occurring mussel, Mytilus galloprovincialis. Either these findings indicated a high capacity for biotransformation of PSP toxins by abalone or that A. catenella was not the source of the toxin. Investigation of the anatomical distribution of toxins revealed that they were not evenly distributed throughout the abalone tissues, but appeared to concentrate in outer layer tissue. The muscular foot made a disproportionately low contribution to the total toxin content of the mollusc, whereas the epipodial fringe, although comprising a small proportion of the abalone total weight, contributed substantially to the total toxin content. The epipodial fringe is typically included with the muscular fool as that part of tile animal marketed for human consumption. The negative impacts of PSP contamination on abalone spawning and larval survival are presented and the findings of this study are compared to observations of PSP toxins in the abalone Haliotis tuberculata on the Galician coast. Theinability of abalone to detoxify or depurate accumulated PSP toxins below the regulatory level threatens the future of the established abalone fishery and the newly developed aquaculture operations on the West Coast of South Africa.