A taxonomic study of cutthroat trout, Salmo Clarki Clarki Richardson, rainbow trout Salmo Gairdneri Richardson and reciprocal hybrids.

Reciprocal hybrid crosses were made of cutthroat and rainbow trout: and the eggs were reared under similar conditions with pure cutthroat and pure rainbow eggs. Viability of hybrid crosses was compared with viability of pure strains, and sex ratios in (offspring) were studied. Relative growth of several head and body parts was studied in the four lots of fish. Meristic comparisons, counts of teeth and pyloric caeca were made. Coloration was studied in all experimental lots of fish. Hybrid crosses were as viable as intraspecific crosses and sex ratios did not differ significantly from expected. Relative growth studies showed cutthroat had larger heads, larger head parts and deeper peduncles than rainbows. Hybrids were usually intermediate. Rainbow trout had higher scale, ray and vertibral counts than cutthroats. Contrary to most authorities, scale counts were higher on rainbows than on cutthroat. Dorsal ray counts for both hybrid lots resembled rainbow parents. Vertebral counts among hybrids tended to resemble female parents. No marked differences were found in teeth except on the hyoid bone. Pyloric caeca counts were similar in both parental lots. Coloration on rainbows was different than on cutthroats. Hybrids were intermediate in some aspects of color and in others they tended to resemble one parent. Eight samples of wild fish were examined. Several features which were distinctive in the hatchery fish were different for the two species in the wild.Science, Faculty ofZoology, Department ofGraduat