A Comparison of the Growth of Vertically-Migrating and Nonmigrating Kokanee (<i>Oncorhynchus nerka</i>) Fry

Abstract

A comparison of the growth of vertically-migrating kokanee (Oncorhynchus nerka) fry and nonmigrating fry confined to the epilimnion in thermally-stratified Kootenay Lake, British Columbia rejected the bioenergetic efficiency hypothesis for the adaptive significance of vertical migration. Growth rates were higher for nonmigrating fry than for vertically-migrating fry. Geometric mean wet weights in early October were 2.88 g for non-migrating fry and 1.40 g for vertically-migrating fry of the same stock. The geometric mean weight of fry of a second stock rearing in the isothermal West Arm, in which behavioural thermoregulation by vertical migration was not possible, was 8.54 g in early October.