The effect of rearing structures on behaviour and movement of juvenile steelhead Oncorhynchus mykiss

Abstract

The relative movement of juvenile steelhead Oncorhynchus mykiss reared on two treatments was investigated to provide insight on the effect of structure in the rearing environment on the behaviour of the fish before potential release into a natural river system. The progeny of wild broodstock were reared either in the presence or absence of structure in the tank environment for 7 months at the Oregon Hatchery Research Center located in Oregon, U.S.A. Behavioural assessments, including movement response to a simulated predator, showed that fish reared on structure moved a similar amount (based on line crosses) as fish reared in bare hatchery tanks. No significant difference was observed in the proportion of time spent near a small structure within the behavioural test tank between the two treatments, but all fish showed decreased movement over time with each subsequent predation event. Fish from both treatments spent 30% of their time in the section of the tank containing the structure, which was one section out of a total of eight sections. In both treatments, fish foraged 20% of the time in the 2 min following the introduction of live tubifex prey (two separate events). Overall, similar movement and foraging responses occurred following mock predation events for juveniles reared either with or without structure. Developing assessment tools such as these, that measures behaviours related to survival based on rearing environment should allow managers to better predict the survival and effect of rearing conditions on the release of hatchery-origin fish into the wild.

Influence of Water Velocity and Vertically-Suspended Structures on Rainbow Trout Rearing Performance

“…Physical enrichment has been intensively studied. Investigators have placed a variety of structures in rearing tanks, including tree roots [2], woody debris [2] [5] [6] [7] [8], rocks and concrete blocks [8]- [14], and imitation aquatic plants [20]. However, most of these structural enhancements are incompatible with production-level hatchery rearing because they interfere with tank hydraulic self-cleaning, subsequently increasing labor demands and creating conditions favorable for disease outbreaks [14] [21] [22].…”

Use of Exercise and Structure during Rainbow Trout Rearing

“…Considerable attention has focused on physical and occupational enrichment. [20] [21]. However, these physical environmental techniques are largely incompatible with production-level hatchery rearing because they impede tank hydraulic self-cleaning.…”

Reared to become wild-like: addressing behavioral and cognitive deficits in cultured aquatic animals destined for stocking into natural environments—a critical review

“…Foraging-related behaviors have been indicated to change in some studies, but results include both positive (Brown et al 2003a, Beck and Rooker 2008, Rodewald et al 2011, Ullah et al 2017, Brignon et al 2018) and negative effects (Moberg et al 2011, Rae et al 2020. Some studies show no detectable differences in foraging between enriched and standard-reared animals (Carrera-García and Rochard 2016, Self et al 2018, Hatanpää et al 2020. Differences in results may depend on a variety of factors, like species autecology (comparative studies are unfortunately lacking), which context an animal is tested in (e.g., threatening or benign contexts, warm or cold water, etc.…”