| Abstract | This study examined the effects of strain and ploidy on the growth of Atlantic salmon Salmo salar post-smolts in a 12-week tank trial, using specific growth rate (SGR), condition factor (CF) and plasma insulin-like growth factor I (IGF-I) as indicators of growth. Five strain/ploidy combinations (“populations”) were evaluated: triploids of two domesticated strains (Canadian-origin “Cascade” and Norwegian-origin “Mowi”) and diploids of the same Mowi strain, a top-performing Bay of Fundy commercial strain derived from St. John River stock (SJR, New Brunswick, Canada) and SJR wild origin. All fish were individually PIT-tagged and then reared in 150 L tanks (3 tanks per population), with individual size measurements recorded every 4 weeks. Wild SJR diploids consistently had the highest SGR, higher even than their domesticated counterparts, and triploid Cascades had the lowest. Ploidy did not affect the SGR of Mowi fish, which tended to be intermediate between wild and domesticated SJR diploids. CF at the end of the study followed a similar pattern, with wild and commercial SJR diploids having the highest CF, followed by diploid Mowi, triploid Mowi and triploid Cascade fish. Plasma IGF-I levels increased from the initial sampling to the end of the growth trial for all populations except the commercial SJR diploids, which maintained the highest levels throughout the study. The observations that (a) there can be significant variation among strains for triploid SGR and (b) some wild strains can outperform their domesticated counterparts as diploids, at least under experimental conditions, provide important information to salmon farmers on the successful use of triploids and the need for continued research into broodstock development. |
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