Comparison of growth, feed intake, and nutrient efficiency in a selected strain of coho salmon (Oncorhynchus kisutch) and its source stock

We compared growth in a domesticated strain of coho salmon (Oncorhynchus kisutch), that had been selected for rapid growth over 16 generations, to that of its hatchery-origin unselected parental stock. Fish were spawned on the same date and incubated under similar conditions. First feeding fry were fed to satiation and then were fed a commercial salmon feed at two ration levels, either to satiation or on a fixed ration from the size at which the smallest fish could accept a 1-mm pellet (domesticated 0.65 g, hatchery 0.96 g). The domesticated fish outperformed unselected fish by growing faster and to a larger size, ingesting a greater amount of feed when fed to satiation, and exhibiting greater efficiency in feed conversion. When fed to satiation, domesticated fish ingested 53% more feed and gained 78% more weight compared to unselected fish. The selected fish also appeared to utilize dietary lipids for energy while sparing protein for growth, while unselected fish deposited dietary lipids as body fat. These results indicate that selection over 16 generations for growth also resulted in changes in feed efficiency and energy allocation. Understanding the mechanisms underlying improved growth will aid future selection studies by identifying multiple targets of selection that contribute most to growth.