Family Dominance at the Fry Stage Weakly Influences Mean Family Body Length at Smolting in Hatchery‐Reared Steelhead

Abstract

Steelhead Oncorhynchus mykiss reared in hatcheries rapidly adapt to captivity. However, the traits under selection in captivity are not well understood. Hatchery‐reared salmonids are generally more aggressive than wild fish. Therefore, it is possible that selection in hatcheries favors increased aggressiveness because aggressive fish may dominate food resources and grow larger, resulting in a fitness advantage at release. We tested whether family dominance at the fry stage correlates with mean family fork length at smolting of the same families raised in a parallel experiment. Family dominance was assessed when families were first interacting with each other as fry. Juveniles in the parallel experiment were raised at high or low density to determine whether the effect of family dominance on mean family fork length was stronger at low density. More‐dominant families were slightly larger at smolting, and the effect changed little between density treatments. Although the effect we observed was modest, these data are consistent with the hypothesis that dominance as fry is a trait under selection in hatcheries. Received April 8, 2016; accepted July 28, 2016 Published online October 7, 2016

Plasticity of Behavioral and Growth Responses to Two Feeding Regimes and Implications for the Domestication of Steelhead Trout

“…In particular, selection for rapid growth rate can occur in as little as one generation of culture (Wilke et al 2015; Horreo et al 2018) and it is presumably caused by size‐selective mortality after release (Clarke et al 2014; Osterback et al 2014; Tatara et al 2017). Growth rate may be linked to behavioral traits, such as feeding activity and aggression (Metcalfe 1986; Metcalfe et al 1986; Abbott and Dill 1989); thus, differences in such traits between hatchery and natural populations may also reflect the domesticating effects of hatcheries that are related to growth rate (Thompson and Blouin 2016). In the case of steelhead Oncorhynchus mykiss , growth rates can be manipulated by adjusting ration levels to induce smoltification after 1 or 2 years of hatchery rearing, depending on program goals, rearing temperature, and spawn timing (USFWS 2009; Berejikian et al 2012; Tatara et al 2017).…”