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. The pattern of significant reductions in velocity with the use of any environmental enrichment, with further significant velocity reductions in the double angle treatment, was repeated when the data were combined for each sampling depth, radius from the center, and degree (circular arc). Although considerable variation in water velocity was observed at each specific sampling location with both incoming velocities, significantly lower velocities were observed at nearly every sampling location with the addition of any environmental enrichment to the circular tank. In addition, the double angle array consistently produced the lowest velocities among the environmental enrichment treatments. The changes in velocity profiles from vertically-suspended environmental enrichment may be at least partially-responsible for the frequently-observed improvements in fish growth.
Highlights
The ideal fish rearing tank would have uniform water quality, be self-cleaning, provide water velocity for fish exercise, and efficiently use the available floor plan
This study examined the tank water velocity profiles of four different vertically-suspended structures and a control at two incoming water velocities (18.3 cm/s and 54.9 cm/s) in 1.8-m diameter circular tanks
The significance level for all tests was predetermined at P < 0.05. At both of the incoming water velocities (18.3 cm/s and 54.9 cm/s), overall water velocities throughout the tank were significantly reduced with the addition of any form of environmental enrichment in comparison to the control tanks devoid of structure (Table 2)
Summary
The ideal fish rearing tank would have uniform water quality, be self-cleaning, provide water velocity for fish exercise, and efficiently use the available floor plan. Circular tanks excel at homogeneously distributing dissolved oxygen, and eliminating biosolids [2] [3] [4], as well as providing adequate velocity for exercise [5] [6] [7] [8]. They cannot share tank sidewalls, precluding optimum space management [9]. Flow patterns are significantly affected by the addition of environmental enrichment structures to the tanks [10]
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