Abstract.- Otolith microchem- 

 istry of anadromous and non-anad- 

 dromous salmonids was investigated 

 to determine if there were differ- 

 ences among migratory and non- 

 migratory individuals and if the 

 habitat where vitellogenesis took 

 place would affect the composition 

 of the otolith primordia of the prog- 

 eny. Electron microprobe transects 

 across salmonid otoliths showed that 

 there were large differences in oto- 

 lith Sr/Ca ratios among adult anad- 

 romous and non-anadromous indi- 

 viduals, but there were no detectable 

 differences in Na/Ca, KJCa, and S/Ca 

 ratios. The hypothesis that Sr/Ca 

 ratios in the primordia of the prog- 

 eny of anadromous salmonids would 

 be greater than those in the primor- 

 dia of the progeny of non-anadro- 

 mous individuals because of differ- 

 ences in the composition of ova was 

 tested and confirmed by the results 

 of a controlled experiment. Also, the 

 ova of anadromous Oncorhynchus 

 mykiss were found to contain 5 times 

 more Sr than their non-anadromous 

 conspecifics. On the basis of these 

 data, it was concluded that otolith 

 nucleus Sr/Ca ratios can be used to 

 distinguish the progeny of sympatric 

 anadromous and non-anadromous 

 salmonids. 



Use of Otolith Microchemistry 

 to Distinguish the Progeny 

 of Sympatric Anadromous 

 and IMon-anadromous Salmonids 



John M. Kalish 



Department of Zoology, University of Tasmania 

 GPO Box 252C, Hobart. Tasmania 7001, Australia 



Present address Fisfieries Researcfi Centre, Ministry of Agriculture and Fisheries 

 P O Box 297, Wellington, New Zealand 



Manuscript accepted 11 June 1990. 

 Fishery Bulletin, U.S. 88:6.57-666. 



The ability to differentiate between 

 juvenile anadromous salmonids and 

 their sympatric non-anadromous con- 

 specifics is essential for management 

 of these species. However, stock dis- 

 crimination between sea-run and res- 

 ident freshwater salmonids has been 

 limited to the adults upon their re- 

 turn from the sea to spawn. Further- 

 tnore, for those species where anad- 

 romy is a facultative, and not an 

 obligate behavior, such as brown trout 

 Salmo trutta, rainbow trout Oncorhyn- 

 chus mykiss, Atlantic salmon Salmo 

 salar, cutthroat trout Salmo clarkii, 

 and Arctic char Salvelinus alpinus, 

 it has been impossible to distinguish 

 between the co-occurring forms on 

 the basis of meristic or mor-phometric 

 characters (Nordeng 1983, Jonsson 

 1985, Neilson et al. 1985). McKern et 

 al. (1974) were able to distinguish be- 

 tween winter and summer races of 

 steelhead trout (anadromous rainbow 

 trout) from rivers in British Colum- 

 bia, Washington, and Oregon on the 

 basis of sagittal otolith nuclear dimen- 

 sions that they believed to be affected 

 by both qualitative and quantative 

 differences in yolk. Rybock et al. 

 (1975) concluded that differences in 

 the size of female resident non-anad- 

 romous rainbow trout and steelhead 

 trout resulted in differences in egg 

 size and, subsequently, the size of the 

 otolith nucleus in the progeny. How- 

 ever, both Neilson et al. (1985) and 

 Currens et al. (1988) found that mea- 

 surements of otolith nuclear dimen- 



sions were of questionable value in 

 distinguishing juvenile non-anadro- 

 mous and anadromous rainbow trout. 

 Development of ova in anadromous 

 salmonids is virtually complete through 

 vitellogenesis or yolk formation be- 

 fore the fish enter freshwater. On the 

 basis of this information, I hypothe- 

 sized that egg composition would, in 

 some way, reflect the chemical com- 

 position of the seawater environment 

 and that this would ultimately affect 

 the composition of the otoliths of 

 the progeny, particularly the otolith 

 nuclei that are formed in the early 

 stages of development and well be- 

 fore yolk utilization is complete. Yolk 

 is formed through the deposition of 

 a phospholipoprotein-calcium com- 

 plex yolk precursor, vitellogenin, in 

 the developing oocyte (Mommsen and 

 Walsh 1988). Solubility and transport 

 of vitellogenin through the circula- 

 tory system of the female and to the 

 developing ovaries may be dependent 

 on the presence of calcium which has 

 been shown to increase markedly in 

 female salmonids (Bailey 1957, Booke 

 1964, Elliot et al. 1979) and other 

 fishes (Ogiu-i and Takada 1967, Wood- 

 head 1968) during gonad develop- 

 ment. Vitellogenin has a high affin- 

 ity for calcium due to the significant 

 negatively-charged phosphate compo- 

 nent of the molecule (Hara and Hirai 

 1978, Hara et al. 1980). The calcium 

 binds to the vitellogenin molecule 

 and, in this complexed form, the vitel- 

 logenin and calcium are deposited in 



657 



