Vertically-Suspended Environmental Enrichment Alters the Velocity Profiles of Circular Fish Rearing Tanks

Abstract

The inclusion of vertically-suspended environmental enrichment in circular tanks has produced substantial benefits during fish rearing. This study examined the tank water velocity profiles of four different vertically-suspended structures (rod array, extended rod array, single angle array, double angle array) and a control (no environmental enrichment) at two incoming water velocities (18.3 cm/s and 54.9 cm/s) in 1.8-m diameter circular tanks. At both of the incoming water velocities, overall water velocities throughout the tank were significantly reduced with the addition of any environmental enrichment in comparison to the control. In addition, the overall water velocities in the double angle array were significantly lower than the other three enrichment treatments.

Rearing Performance of Atlantic Salmon Grown in Circular Tanks with Vertically-Suspended Environmental Enrichment

“…The vertically-suspended environmental enrichment maintained the self-cleaning nature of the circular tanks, as has also been reported by Kientz and Barnes [18], Kientz et al [19], and White et al [22]. Although other types of vertically-suspended arrays have been shown to decrease velocities below the level needed for hydraulic self-cleaning [29], the structure used in this study is acceptable for use in production fish hatcheries where circular tanks must be self-cleaning.…”

“…The alteration of water velocity behind the suspended conduit array may be responsible for the positive affect on Atlantic salmon feed conversion ratio observed in this study. Moine et al [28] and Muggli et al [29] reported that vertically-suspended structure arrays produce significant changes in circular tank water velocity profiles, with decreased water velocities behind the arrays. These lower velocity microhabitats likely positively influence fish energy expenditure [18] Routine fish husbandry demands were not negatively affected by the use of the conduit arrays in this study.…”

Use of Two Vertically-Suspended Environmental Enrichment Arrays during Rainbow Trout Rearing in Circular Tanks

“…Vertically-suspended environmental enrichment dramatically changes circular tank flow dynamics [25,26]. These changes likely lead to bio-energetic benefits by creating lower velocity microhabitats favorable to juvenile salmonids [27].…”

“…These changes likely lead to bio-energetic benefits by creating lower velocity microhabitats favorable to juvenile salmonids [27]. In addition, fish reared with angle arrays may be benefitting from periodic exercise [26]. Fish benefit from higher velocity-induced exercise during hatchery rearing [4,[28][29][30].…”

“…Thus, there appears to be upper limits on the amount of vertically-suspended structure that can be used to improve fish rearing performance. Simply addition extra structures to fish rearing tanks does not appear to positively affect the fish and can actually negatively affect the tank environment by eliminating or reducing circular tank hydraulic self-cleaning [19,26,33].…”