The mismatch between swimming speeds and flow regimes when optimising exercise regimes to improve Chinook salmon, Oncorhynchus tshawytscha, performance

Exercise regimes provide a promising opportunity to enhance production performance during hatchery rearing, but exercise-enhanced traits are presently poorly understood in Chinook salmon. In addition, spinal health can be a concern in some farms in New Zealand and unfavourable correlations between higher condition factor and spinal curvature have been detected. Exercise regimes, in other salmonids, have improved bone mineralisation and lowered condition factor. Therefore, we hypothesise that sustained swimming could be used as a tool to improve spinal health. Here we tested the influence of low (0.3 bl s-1) and moderate (0.8 bl s-1) flow regimes on post -smolt (initial size: wet weight = 82.9 +/- 0.3 g, fork length = 174.6 +/- 0.2 mm) Chinook salmon feed efficiency and growth performance, as well as spinal health. We first measured the actual swimming speeds of Chinook salmon under low and moderate flow regimes to determine differences in exercise levels. Swimming speeds were not different between the flow regimes and were much higher than the set flow, because the Chinook salmon were advancing around the tank, swimming faster than the set flow at their own chosen swimming speed. Moderate flow regimes improved feed efficiency but did not influence other feed and growth metrics or spinal curvature and vertebral anomalies prevalence or severity. Production performance significantly differed between individuals with normal spinal health and those that developed spinal anomalies (vertebral compression, -fusion, and/or -vertical shift) or spinal curvature (lordosis, kyphosis, and/or scoliosis). Chinook salmon that developed spinal anomalies were smaller, grew slower, and exhibited poorer feed efficiency, whereas individuals that developed spinal curvature were significantly heavier, longer, and had higher condition factor. The probability of individuals developing spinal curvature increased with higher condition factor. These results provide critical information for industry to consider in their selective breeding objectives to curb the prevalence and severity of spinal curvature incidences.