Physiological Tools for Evaluating Growth Status of Migrating Salmon

Abstract Excerpt:
Growth-dependent mortality of juvenile salmon during the early phase of their marine life has been an active area of research. Although the exact timing and the extent of growth-dependent mortality are not clear (Beacham et al. 2017), the general belief is that large and/or fast-growing juveniles have a better chance to survive and will be recruited to the stock (Beamish and Mahnken 2001). Monitoring growth status of out-migrating juveniles is therefore of particular importance. However, a direct measure of growth of individual fish requires marking and recapture of the same individuals, which is extremely difficult to conduct on free-swimming salmon. Instead, indirect methods are often used to evaluate/estimate growth. Among them, scales and otoliths are useful to reconstruct past growth patterns and habitats. However, they may not provide information on the recent/current growth rate. Biochemical growth indices such as muscle RNA/DNA ratio have been used to monitor recent/current growth, although their validity is somewhat incomplete (Johnson et al. 2002). Ideally, growth indices should be directly involved in the growth process and not a result of growth (Couture et al. 1998).