Differences in Incubation Period and Survival of Embryos among Brook Trout Strains

Abstract

The incubation period and survival of brook trout Salvelinus fontinalis embryos were compared among four genetically different strains: Temiscamie (Quebec), Assinica (Quebec), Horn Lake (Adirondack), and Little Tupper Lake (Adirondack). Eggs were fertilized and then incubated under cold (mean, 5.1°C) and warm (mean, 9.4°C) thermal regimes, and the accumulated degree-days and days to 100% hatch were recorded. Within all strains, embryos incubated under the warm thermal regime accumulated more degree-days to 100% hatch than embryos incubated under the cold regime. Degree-days to hatch differed between the two thermal regimes, ranging from 457 to 672 (P < 0.001). Mean degree-days to hatch also differed among strains (P < 0.001). Under the cold regime, Assinica strain embryos developed the fastest and hatched after the fewest degree-days (457), whereas Temiscamie strain embryos developed the slowest (549 degree-days). The two Adirondack strains developed at similar rates (Horn Lake, 486 degree-days; Little Tupper Lake, 490 degree-days). Under the warm regime, Assinica and Temiscamie strains developed the slowest (672 and 654 degree-days, respectively), whereas the Adirondack strains developed the fastest and at similar rates (Little Tupper Lake, 588 degree-days; Horn Lake, 593 degree-days). The Assinica strain embryos incubated in cold and warm thermal regimes showed identical times to 100% hatch (91 d). The other three strains hatched from 8.5 to 12.5 d sooner in the warm regime than in the cold regime. Survival among the four strains was lower at 9.4°C (40–57%) than at 5.1°C (60–73%; P < 0.001). The differences in incubation period were likely caused by genetic differences among strains because the groups of embryos were incubated in physically identical environments with a common water source. The similarity in embryonic development between the two Adirondack strains may reflect an important local geographical adaptation different from that of the Quebec strains, which originated from more northerly populations.