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The effect of different light intensities (0, 15 and 200 lux) over a fish tank and a voluntary fish transport canal was studied. The experiments were carried out in an experimental plant where the fish tanks are connected to a transport canal with gates located at the bottom of the fish tanks. By using different light intensities over the fish tank and over the transport canal, the voluntary fish transport from the fish tank into the canal started quicker than in the control groups, where equal light intensity was used over the tank and canal. The best result was achieved by decreasing the light intensity over the fish tank from the normal 15 lux to almost black (0 lux), and using normal light intensity (15 lux) over the canal. After 30 min, 74·3% of the fish had moved from the tank into the canal, while only 27% of the fish in the control group had moved through. Lowering the light intensity in the canal and/or increasing the light intensity over the fish tank resulted in only a small portion of the fish entering the canal. After 30 min on average only 15–17% of the fish had gone through under these conditions. |
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