CAN INGESTED CYANOBACTERIA BE HARMFUL TO THE SIGNAL CRAYFISH (PACIFASTACUS-LENIUSCULUS)

1. A sample of adult signal crayfish were taken from a pond with a hep atotoxic bloom of the benthic cyanobacterium Oscillatoria sancta. Cyan obacteria were found in the stomachs of thirty-one out of thirty-two c rayfish examined. 2. To examine the effect of hepatotoxic cyanobacteri a on crayfish a 14-day feeding trial was carried out with thirty-six a nimals. There were three treatments: (i) hepatotoxic and (ii) non-toxi c Planktothrix agardhii; and (iii) crayfish pellets as a control. 3. H igh-performance liquid chromatography (HPLC) showed that microcystins (the toxins of P. agardhii) had accumulated in the hepatopancreas of 5 0% of the animals in the toxic treatment. 4. The cyanobacteria did not appear to have any negative impact on the crayfish. All crayfish surv ived, remained motile and ate throughout the experiment. 5. During the experiment blood samples were taken and the total number of haemocyte s counted. At the end of the experiment glucose concentration and rela tive wet weight of the hepatopancreas were measured. No differences be tween crayfish fed on toxic and non-toxic P. agardhii and the controls were found. 6. The fact that microcystin accumulates in the crayfish hepatopancreas indicates that the toxin may be transferred further up the food chain.