NOTE Ennevor: Marking Oncorhynchus kisutch fry 



473 



Coho salmon fry exposed to 50 ugL -1 of lantha- 

 num or cerium daily resulted in higher levels of ac- 

 cumulation than fry exposed intermittently to con- 

 centrations of 100 ug-Lr 1 or 150 ug-L -1 . In tanks with 

 higher concentrations, number of mortalities in- 

 creased as deposition of the elements in the verte- 

 bral column decreased. Therefore, toxicity and accu- 

 mulation may be related to element concentration 

 during treatments rather than accumulated expo- 

 sure. A high concentration of lanthanides may im- 

 pair gill function and prevent further uptake of lan- 

 thanides, as well as essential ions and oxygen 

 (BehrensYamada and Mulligan, 1990). Consequently, 

 marking with a low concentration of lanthanide over 

 an extended period is highly recommended. 



A potential concern is the ability to detect the lan- 

 thanide mark in the bony tissues of returning adults. 

 Because fish continually accumulate calcium in their 

 bony tissues after marking, the relative amount of 

 lanthanum or cerium will decline gradually as the 

 fish grows (Behrens Yamada et al., 1979; Behrens 

 Yamada and Mulligan, 1982). Marks laid down dur- 

 ing freshwater growth stages will be concentrated 

 in the center portion of bony tissues. A possible solu- 

 tion to this dilution problem is to analyze only the 

 center where the element concentration would be 

 about the same as when marked (Behrens Yamada 

 and Mulligan, 1982). Scales of returning adults may 

 be more suitable for sampling and analysis as they 

 retain higher lanthanide concentrations (Ennevor 

 and Beames, 1993). Also, scales are easier for sam- 

 pling and can be removed for lanthanide determina- 

 tion without sacrificing the fish. 



These studies demonstrate the successful mark- 

 ing of experimental groups of fry with lanthanum 

 and cerium applied through the water supply. This 

 technique can be adapted to mark large groups of 

 juvenile salmon at hatchery stages quickly and effi- 

 ciently without affecting growth or survival. Mass 

 marking with lanthanides can mark large groups of 

 fish for identification without apparent deleterious 

 effects. In addition, the mark remains in the bony 

 tissues for extended periods of time, and samples of 

 bony tissues (i.e. scales and opercular punches) can 

 be taken from marked fish, without sacrificing the 

 fish, for identification by ICP-MS analyses. 



Acknowledgments 



I am grateful to K. R. Pitre, E. A. Perry, and F. K. 

 Sandercock for their helpful comments on the manu- 

 script. The assistance of staff and the facilities ex- 

 tended by Capilano Hatchery during the course of 

 the'-e experiments are appreciated. Thanks also go 

 to R. Brown and his staff at Elemental Research Inc. 

 who performed the ICP-MS analyses. Finally, I wish 



to acknowledge the continued financial support of 

 the Department of Fisheries, Canada. 



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