Vertically-Suspended Environmental Enrichment Structures Improve the Growth of Juvenile Landlocked Fall Chinook Salmon

Environmental enrichment is the addition of structures or materials to create a more natural or complex environment in otherwise stimuli-deprived hatchery rearing units. It has been used in an attempt to improve post-stocking survival (Berejikian et al. 1999; Fast et al. 2008), but some forms of enrichment have also shown the potential to improve foraging efficiency, reduce fin damage, and promote greater social dominance in hatchery-produced fish (Bosakowski and Wagner 1995; Berejikian et al. 2001; Rodewald et al. 2011). Structural additives meant to imitate natural environments, including sand and gravel substrates, stones, woody debris, and live prey have been common methods of enriching rearing tanks and raceways (Brown et al. 2003; Brockmark et al. 2007). However, the use of natural substrates and structures can impede circular tank hydraulic selfcleaning, increasing the time required to perform routine culture activities and also creating conditions favorable to pathogenic bacteria (Baynes and Howell 1993; Tuckey and Smith 2001; Krebs et al. 2017).