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The effect of space at constant densities on growth in a cichlid Aequidens pulcher Gill Minchin, J. Daniel deC. E.

Abstract

The effect of impoundment size on fish has been investigated. Investigators have reported that greatest growth has taken place in large in some instances and in small impoundments in others. The effect of varying space on the cichlid Aequidens pulcher Gill, was examined in four tanks of equal volume. Each tank was divided into two replicates in the compartment ratios 9:3:1 and each contained 90:30:10 fish respectively. A higher density tank had twice the fish number in all compartments and had lowest growth due to either reduced oxygen availability, increased biomass, increase in activity or stress due to small nearest neighbour distances. Fish in a tank with mirrors on all compartment walls had a reduced growth possibly due to visual stress compared to a control lacking mirrors. A further tank had twice the surface area of the control, a greater distance between nearest neighbours and greatest fish growth. Growth was significantly greater, at the 95 percent confidence limit, in all small compartments of tanks and activity was significantly greater in large compartments. In an identical treatment design to that of the control fish were shown to lose weight while being starved. The fish in the larger compartments were more active and lost most weight. A strong suggestion that the lower growth rate in large compartments was due to greater activity, possibly this was related to the total available swimming space per fish. Fish aggression was greatest in small compartments and decreased over time, possibly as a result of conditioning.

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