THE EFFECT OF DOMESTICATION ON SOME LIFE-HISTORY TRAITS OF SEA-TROUT AND ATLANTIC SALMON

During the period 1968-1991, certain morphological traits of Atlantic salmon Salmo salar and sea trout S. trutta have been recorded regularl y at the hatchery al Alvkarleby, central Sweden. Total body length, we ight (for females both before and after stripping), number of eggs, eg g size and date of ovulation. A smaller data set for fish marked and r eleased as smells, providing information about total body length of re leased smelts, time spent at sea and body size of the recovered adults , was also available for analysis. According to theory and empirical d ata, the process of artificial breeding results in an evolutionary div ergence of the cultured strain from the wild phenotypic norm. The reas on for such a divergence is that both natural and sexual selection pre ssures are altered or relaxed during the process of artificial breedin g, as well as random genetic processes, such as founder effects and in - and outbreeding. A path analysis of both species and sexes revealed that the size of the released smelts had increased during the study pe riod. Time spent in sea has decreased for both female and male sea tro ut, but not for Atlantic salmon. Adult body size for female and male t rout have increased as well as female trout condition Factor. The incr ease found in egg size of both species was greater for the salmon than for the trout, indicating that female salmon invest more in egg size with increasing body size. These results support the view that domesti cation probably has a significant and selective impact on the life his tory traits of the two salmonid species studied. (C) 1996 The Fisherie s Society of the British Isles