Impact of Vertically-Suspended Environmental Enrichment and Two Densities of Fish on Circular Tank Velocity Profiles

Abstract

Vertically-suspended environmental enrichment has been shown to produce improvements in fish growth during hatchery rearing in circular tanks. This study documented the effects of a novel suspended structure on the velocity profile of a 3.63-m diameter circular tank containing juvenile landlocked fall Chinook salmon (Oncorhynchus tshawytscha) at two different densities (9.0 and 34.3 kg/m 3). The addition of vertically-suspended structure to the tank significantly decreased velocities at nearly every sampling point, with velocities typically dropping from 15 cm/s without structure to less than 6 cm/s when structure was present. Fish density also significantly impacted in-tank velocities, with an inverse relationship observed between the density of fish and water velocity. Significant interactions were present among the presence or absence of structure and fish density. When structure and fish were absent, the velocity at the edge of the tank was 15.63 cm/s, which was significantly higher than the 4.75 cm/s velocity when both structure and the lower fish density were added, which was in turn significantly higher than the 2.29 cm/s velocity observed with structure and higher fish density. Despite the potentially unique features of this study, vertically-suspended environmental enrichment and the presence of fish clearly alter circular tank water velocities, which may at least partially explain the improvements in fish rearing performance observed with the use of suspended structure.

Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

“…In this context, even if structural enrichment does not provide shelter, it can simply add environmental complexity and heterogeneity that can also improve the welfare conditions of captive fish. For example, adding vertically‐suspended structures can modify the water flow and velocity profiles in fish tanks, 54,55 and it has been demonstrated that substantial benefits can be accrued during rearing of four salmonid species. Jones et al 56 demonstrated that feed conversion rate can be improved in Atlantic salmon by inserting an array of suspended plastic conduits in the rearing tank, but did not report significant differences in individual fish length, total weight gain, individual weight or condition factor.…”

Exercise and Structure Improve Juvenile Chinook Salmon Rearing Performance

“…However, these velocities were taken prior to structure and fish being added to tanks. Vertically-suspended structure radically changes and typically decreases circular tank water velocities [65] [66] [67], and the presence of fish alter velocity profiles as well [67] [68]. It is possible that the positive effect on gain observed in the tanks receiving both exercise and structure, in comparison to the lack of effect of just exercise, could be due to the water velocity changes caused by the aluminum angle array [35].…”