Social dominance, growth, and habitat use of age-0 steelhead (Oncorhynchus mykiss) grown in enriched and conventional hatchery rearing environments

Abstract

This study investigated whether culturing age-0 steelhead (Oncorhynchus mykiss) in habitat-enriched rearing tanks, containing a combination of in-water structure, underwater feeders, and overhead cover, affected competitive ability and habitat use compared with juveniles cultured in more conventional vessels. In laboratory tests, steelhead juveniles grown in the enriched tanks socially dominated size-matched competitors grown in conventional tanks. When both treatments were introduced into separate sections of a quasi-natural stream, no differences in growth were found between them. However, when intermixed, fish reared in the enriched tanks grew at a higher rate than conventionally reared competitors, suggesting greater competitive ability of juveniles grown in the enriched tanks. Visual isolation and defensible food resources in combination in the enriched tanks were considered as the primary factors causing the observed competitive asymmetries. Steelhead juveniles from the two rearing environments exhibited very similar use of woody structure in the quasi-natural stream, both in the presence and in the absence of mutual competition. Rearing steelhead in more naturalistic environments could result in hatchery fish that behave and integrate into the postrelease (natural) environment in a manner more similar to wild fish.

Use of Bottom Structure and Tank Cover during Rainbow Trout Rearing in Circular Tanks

“…These results are similar to Brockmark et al [9], who found no significant difference in fish rearing performance with the addition of plastic plants and rocks to tank bottoms. Although neither this study nor Brockmark et al [9] found significant benefit with the use of environmental enrichment, benefits from the addition of structure in tanks has been found in other studies [2,6]. One difference that could account for the significant results of Kientz and Barnes [6] is the placement of structure in the tank.…”

“…The use of environmental enrichment can be beneficial during salmonid rearing [2,6], but not all enrichment techniques are equally effective in improving fish rearing performance. The use of concrete blocks on tank floors as a method of enrichment is not recommended because of a lack of significant effect on fish growth, as well as increased demands on routine cleaning.…”

“…Previous studies examining environmental enrichment techniques have noted that the addition of structure may increase competitive behavior and foraging skills in domesticated fish [2][3][4] as well as improve fish swimming ability and adaptability to new environments [5]. Vertically-suspended structure has also been observed to improve fish weight gain during hatchery rearing [6].…”

“…For example, many studies have placed natural materials such as woody debris, plants, and root wads on the bottom of hatchery rearing tanks [2,[7][8][9][10][11], but those materials may interfere with the self-cleaning nature of circular rearing tanks by altering water flow patterns. This leads to more frequent tank cleanings because of an increase of food and feces trapped in structures [12].…”

Enrichment promotes learning in fish

“…Recent work has shown that the development of various fish behaviours are influenced by the experience of environmental complexity , Braithwaite 2006. Berejikian et al (2000Berejikian et al ( , 2001 have reported that rainbow trout Oncorhynchus mykiss reared in enriched environments were socially dominant to size-matched fish reared in plain environments. In juvenile Atlantic cod Gadus morhua, experience with spatial structures in the nursery environment increased behavioural flexibility , Salvanes et al 2007).…”