Behavior of Steelhead Fry in a Laboratory Stream is Affected by Fish Density but Not Rearing Environment

Abstract

We quantified the aggression, feeding, dominance, position choice, and territory size of naturally reared steelhead Oncorhynchus mykiss fry stocked with two types of hatchery‐reared fry (from conventional and enriched rearing environments) at two densities in experimental flumes to determine how rearing environment and fish density affect the behavior of steelhead fry. We found that fry density had a significant effect on most response variables but that rearing treatment did not. The rates of threats and attacks were positively correlated with fry density, but the overall feeding rate was negatively correlated. Naturally reared fry were dominant more often at low densities, and hatchery‐reared fry were dominant more often at high densities. There were no significant effects of hatchery rearing treatment on aggression, feeding, dominance, or territory size. The only significant effect of rearing treatment was on the position of naturally reared fry, which occupied more upstream positions when stocked with conventional than with enriched hatchery‐reared fry. Overall, rearing environment had relatively little influence on the behavior of steelhead fry. Our results indicate that stocking hatchery‐reared steelhead fry at low densities may have effects on similar‐size wild fish comparable to an equivalent increase in the density of wild fish. We suggest that releasing hatchery‐reared steelhead fry as a supplementation strategy may have few direct negative ecological effects on wild fry.

Environmental enrichment for fish in captive environments: effects of physical structures and substrates

“…, , ; Riley et al . , ; Berejikian and Tezak ; Kihslinger et al . ; Gerasimov and Stolbunov ; Tatara et al .…”

“…Many studies have used non-factorial experimental combinations of submerged structures along with underwater feeders, tank covers, natural food, predation simulation and varying water current and depth (Berejikian et al 1999(Berejikian et al , 2000(Berejikian et al , 2001Riley et al 2005Riley et al , 2009Berejikian and Tezak 2005;Gerasimov and Stolbunov 2007;Tatara et al 2008Tatara et al , 2009Fast et al 2008;Roberts et al 2011;Rodewald et al 2011;Hyv€ arinen and Rodewald 2013). Effects of the treatments differ, probably due to enrichment type, species and life stage differences.…”

Silver spoons in the rough: can environmental enrichment improve survival of hatchery Atlantic salmon Salmo salar in the wild?

“…Enrichment can affect both cognition and competitive ability in fishes (Nijman & Heuts, ; Salvanes & Braithwaite, ; Salvanes et al , ), and both mechanisms may have played a role in this study. For example, steelhead trout O. mykiss (Walbaum 1792) reared in naturalized environments are more aggressive and tend to outcompete similar‐sized conspecifics grown in conventional hatchery tanks (Berejikian et al , , ), although such behavioural differences may not be manifested in the presence of wild fish (Tatara et al , , ; Riley et al , ). It is therefore possible that enriched fish in the study reach (which was inaccessible to wild fish) may have been able to outcompete control fish from the more favourable habitats, thereby achieving a survival advantage.…”

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

“…Studies have found hatchery juveniles to be more dominant or aggressive than wild juveniles (Weber and Fausch 2003), but this is not a universal result (Berejikian et al 1996;Riley et al 2009). Furthermore, the relationship between growth and dominance or aggression can be context dependent.…”

“…In a hatchery environment, rearing density may have a strong impact on the magnitude of the advantage for dominant individuals. For example, hatchery steelhead have been shown to be more aggressive and to dominate wild fish at high densities but not at low ones during the fry life stage (Riley et al 2009). At low densities dominant individuals may be better able to control subordinates and monopolize food resources (Alanärä and Brännäs 1996;Brockmark and Johnsson 2010), while at higher densities scramble competition and/or shadow interference may reduce the payoff to being dominant (Johnsson et al 2014).…”