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Growth rates of Babine Lake underyearling sockeye salmon (Oncorhynchus nerka) fed rations of zooplankton of 14–84 cal/kcal sockeye∙d−1 (1 cal = 4.1868 J; 1.3–7.8% of dry body wt) were determined at constant temperatures of 6.2, 11.3, 15.3, and 15.9 °C, and under a cyclic temperature regime similar to that encountered during their diel vertical migrations. Growth of fish fed rations of 43–76 cal/kcal∙d−1 (4.0–6.9% of dry body wt) was equal or greater under cyclic temperatures than constant temperatures. At the lowest and highest rations growth was greater, respectively, under the constant low temperature and the constant high temperature than under cyclic temperatures. Gross growth efficiency, ranging from < 1 to 31%, was affected by temperature and ration in much the same way as growth. Young sockeye ingesting moderate rations comparable to those probably available in the relatively warm surface layers of Babine Lake, and undergoing diel migrations from deep cold waters to the surface, and return, are likely to grow more rapidly and efficiently than fish maintained at constant temperatures. The selective value of vertical migrations in thermally stratified waters may have an energetic basis as suggested by some other workers.Key words: sockeye salmon, growth rate, conversion efficiency, diel vertical migration, temperature, zooplankton ration, diel cyclic temperature

Rainbow trout (Salmo gairdneri) populations of the Great Lakes showed a great variability in timing of spawning migrations and life histories. This variability was examined to determine if rainbow trout populations of the Great Lakes are comprised of discrete stocks. Differences in timing of migration and spawning indicated that at least one spawning population may be distinctive and that others may be in progressive stages towards emergence of discrete stocks. The innate ability of this species to adapt to different environmental conditions, together with its ability to 'home,' provide rainbow trout in the Great Lakes with the potential to develop discrete stocks. The management of this species that allows for the development of this potential is emphasized.Key words: rainbow trout. Great Lakes, stocks, migrations, spawning, life histories, homing

1980. The fate of I4C labeled food ingested by underyearling sockeye salmon, Oncorl~ynchus t~c r~a , in relation to temperature and ration. Can. J. Fish. Aquat. Sci. 37: 1184-1 192. Underyearling sockeye salmon (Otlcorh-vnchrts nerkn) provided rations likely available in nature grow more rapidly when held under cyclic than under constant temperature. The basis of this enhancement was investigated by following the short-term fate of labeled food in young sockeye fed low (3.4'4 dry body wt/d) and moderate (6.4% dry body wt/d) rations and maintained under conntant and cyclic temperatures. These experiments, corrected for low 14C measured rates of respiration, indicated that growth potential of young sockeye is greater under cyclic temperatures because of the higher respiration rates at constant high temperatures and the greater rates of defecation and excretion at low temperatures. The difficulties in estimating respiration rates from I4CO measurements are emphasized. RIEITE, R. M., AND G. H. GEENE. 1980. The fate of 14C labeled food ingested by underyearling sockeye salmon, Oncorl~yncl~us nerka, in relation to temperature and ration. Can. J. Fish. Acluat. Sci. 37: 1184-1192.Des saumons nerka (Oncor&ync~hus ncrku) de moins d'un an auxquels on a donnC des rations susceptibles cie se trouver dans la nature croissent plus rapidement lorsque mai~ltenus A une temperature cyclique plutdt qu'h une temperature uniforme. LC fontfement de cette acc616ration a 6tC Ctudie par l'observation du sort, 2 court terme, d'une nourriture marquee chez des jeunes saumons nerka nourris de rations faibles (3,47{, du poids corporel sec/jour) et rnodCrt.es (6,4(;j du poids corporel sechour) et maintenus a des tempkratures uniformes et cycliclues. Ces experiences, corrigkes pour tenir compte de faibles taux de respiration mesurks au 14C, indiquent clue le potentiel de croissance des jeunes saumons nerka est rehausse par des temperatures cycliques parce que, h dc hautes temperatures uniformes, les taux de respiration sont plus elevks, et qu'8 de basses temperatures, les taux de dkfkcation et d'excretion sont Cgalement plus elevds. On fait ressortir les difficultes de l'estimation des taux respiratoires A partir de mesures de ' "0 2.