Early survival and development of coastal cutthroat trout (<i>Oncorhynchus clarki clarki</i>), steelhead (<i>Oncorhynchus mykiss</i>), and reciprocal hybrids

Abstract

We compared the survival and development of embryos from fertilization to emergence of two populations of coastal cutthroat trout (Oncorhynchus clarki clarki), one population of steelhead (Oncorhymchus mykiss), and their reciprocal hybrids under controlled conditions (10 ± 1°C). The egg weight of the steelhead (0.110 ± 0.008 (SE) g) was nearly twice that of coastal cutthroat trout (0.056 ± 0.003 and 0.051 ± 0.001 g for the two populations). Fertilization success, survival, duration of hatching and emergence periods, yolk absorption relative to total alevin weight, and yolk conversion efficiency were similar among the cross types. There was no evidence of reduced hatchability or viability of hybrids despite maternal and paternal species effects on size and development. Fish with cutthroat dams had lower percent hatch, were smaller at hatch and emergence, grew more slowly, used less yolk per day, reached 50% yolk absorption earlier, and had a smaller percent yolk at hatch than those fish with steelhead dams. Fish sired by cutthroat males hatched and emerged earlier and took less time between the two stages than fish sired by steelhead. As a consequence, hybrids with cutthroat dams emerged late and had little yolk, while hybrids with steelhead dams emerged early and had an abundance of yolk.