A Comparative Study of Anadromous and Freshwater Populations of Brook Trout (Salvelinus fontinalis (Mitchill))

Anadromous and freshwater populations of Salvelinus fontinalis have been compared to determine the taxonomic relationship of the sea trout and brook trout. Sea trout and freshwater trout differ seasonally in coloration and flesh colour but these differences appear to be environmental in origin rather than hereditary. Freshwater trout reared to hatching at 5.5 °C. had larger head parts, deeper and wider bodies, longer fins, more pectoral rays, dorsal rays, and branchiostegals but fewer scale rows and anal rays than those of common parentage reared at 0.9 °C. Sea trout and freshwater trout from the same river differ less in body form than trout of common parentage reared at different temperatures and less than four populations of freshwater trout. Differential development of the secondary sexual characteristics accounts for most of the differences in body form between sea and freshwater trout. Sea trout and freshwater trout from different rivers reared under the same conditions differed less in body form than any of the other populations compared. Sea and freshwater trout did not differ significantly in any of the meristic structures counted. Seasonal differences in weight-length relationship related to spawning and feeding habits were observed. Sea trout grow rapidly during the year in which they first migrate to the sea but subsequent growth is not appreciably faster than freshwater trout from the same river. Exposure of freshwater trout to sea water indicates that some could survive typical sea trout migrations. No evidence was obtained to indicate hereditary differences in migratory behaviour. Evidence available indicates that sea and freshwater trout of Moser River, Nova Scotia, constitute one taxonomic unit.