Discussion 



The fact that toxin was distributed throughout 

 the bodies of the clams, rather than being concen- 

 trated in the siphons, indicates that the contact 

 between the clams and the toxin-producing or- 

 ganisms had been recent. The lack of a concentra- 

 tion of toxin in the siphon may even indicate that 

 toxification was in progress (Quayle 1969). The high 

 toxin levels in mussels also reinforces the 

 probability that toxification had occurred recently; 

 mussels lose their toxin rapidly (Prakash et al. 1971) 

 and the high levels indicate that the toxicity was 

 acquired shortly before our sampling. 



There is presently no information on the pump- 

 ing rate, particle retention, or assimilation 

 efficiency of Saxidomus giganteus (K. Chew pers. 

 commun.). Pumping rates of the American oyster, 

 Crassostrea virgi)iica,ca.n be as high as 20 liters/h 

 and probably average about 10 liters/h (Loosanoff 

 and Engle 1947; Galtsoff 1964). By using the rate 

 of 10 liters/h, which is conservative for the larger 

 S. giganteus, and assuming a particle retention of 

 25%, which is also conservative when particles the 

 size of G. catenella, 25-55 jum, are ingested (Loo- 

 sanoff and Engle 1947), a toxification period may 

 be calculated. 



Approximately 3,000 G. catenella will produce 

 one mouse unit (approximately equal to 0.2 i-tg) of 

 toxin (see discussion in Neal 1967). Filtering 10 

 liters/h of water containing 235,000 G. catenella 

 /liter and retaining 25% of the G. catenella will 

 result in an increase of 40 jug of toxin/h in each 

 clam. The Saxidomus sampled at Tenakee con- 

 tained 4,500 jug/100 g or approximately 2,250 

 jLig/clam (an average clam probably weighs less 

 than 50 g). Thus, using these conservative figures, 

 it would have taken slightly more than 2 days (57 

 h) of filtering to reach the levels found in Tenakee 

 clams. 



From the known background of this event, it is 

 apparent that the shellfish must have become toxic 

 shortly before the illnesses were reported. The 

 occurrence of the G. catenella bloom approximate- 

 ly 1 wk before the PSP outbreak indicates that 

 even though this species is normally found in very 

 low densities in Alaska, it can occur in high enough 

 numbers to rapidly toxify clams. 

 Acknowledgments 



Donald Gerber and William Goodman, Alaska 

 Department of Health and Social Services, made 

 their investigation of the Tenakee outbreak 



available to us. Louisa Norris and Richard Norris, 

 University of Washington, confirmed the iden- 

 tification of Gonijaulax catenella. Kenneth Chew, 

 University of Washington, provided a very ben- 

 eficial description of the present status of research 

 on Saxidomus giganteus and PSP. 



Literature Cited 



Chang.J.C. C. 



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Steven T. Zimmerman 



Northivest Fisheries Center Auke Bay Fisheries Laboratory 

 National Marine Fisheries Service, NOAA 

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Robert S. McMahon 



Alaska Department of Environmental Conservation 

 Pouch 0, Juneau, AK 99801 



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