Long-term sustained swimming improves swimming performance in Chinook salmon, Oncorhynchus tshawytscha, with and without scoliosis

Exercise training during pre-and post-smolt production is becoming a key component in salmon hatcheries as it is known to enhance several production-related traits in salmonids. Exercise conditions for rearing salmonids are continually being optimised and now that the salmonid industry is developing offshore, training is being considered as a tool to prepare domestic stocks for high energy environments. It is unknown if exercise can enhance traits in other understudied salmonid species and in individuals with spinal curvature (scoliosis), which is a common health concern within some salmon farms. Here we exposed Chinook salmon (initial weight: 82.9 +/- 0.30 g) to low (0.3 bl s-1) and moderate (0.8 bl s-1) flow regimes for ten to eleven months and quantified respiratory and swimming performance in individuals with and without mild scoliosis. Further, we investigated compositional changes and morphological responses at cellular and whole-body levels. Raising Chinook salmon under moderate flow regimes improved critical swimming speed, maximum metabolic rate, and aerobic scope in individuals with and without spinal curvature, but recovery processes (exhaustive exercise post oxygen consumption and time) in individuals with spinal curvature required higher energetic costs (measured immediately after reaching critical swimming speed). Fat content was reduced in fish raised under moderate flow regimes, while protein content was higher in individuals with spinal curvature. Exercise regimes caused morphological changes in muscle fibres, gill, and skin. Together, the results of this study shows benefits for integrating exercise training into hatchery settings (i.e., pre- and post-smolts) to prepare stocks for offshore farming and provides evidence that some exercise-enhanced traits can be translated into individuals with spinal curvature, but concerns remain for individuals with more severe spinal curvature. Additionally, this study reveals that exercise regimes influence nutrient utilisation and deposition in Chinook salmon, therefore optimising nutrient profiles for offshore feeds should be considered as nutrient demands in fish farmed in high energy sites may differ to nutrient demands of fish in lower energy nearshore farms.

Automated summary

Exercise training is important in salmon hatcheries for enhancing production-related traits. Moderate flow regimes can improve swimming and metabolic performance in Chinook salmon, including those with spinal curvature. Exercise regimes also lead to morphological changes in muscle fibers, gill, and skin. This study highlights the benefits of exercise training in hatchery settings and provides insights into nutrient utilization in salmon farming.