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Summary

An experimental approach was used to analyze preferences of the burbot (Lota lota) with regard to water depth, substrate type and flow velocity. In total, 30 burbots used in the experiments were caught in the middle reaches of the River Elbe by electro-fishing. Immediately after capture, they were placed in a 180 L transportation box with aerated freshwater and taken to the research aquarium of the Zoological Museum Hamburg where they were divided into two groups according to total length: group I, 10.0–16.5 cm; group II, 20.0–30.0 cm. Prior to the experiments the fish were adapted to laboratory conditions for four weeks at 20°C in four tanks, each containing 720 L water. For each experiment, three L. lota were transferred to an additional 1350 L experimental tank. After a one-day adaptation phase each experiment ran for three continuous day and night phases. Burbot preferences were tested for (i) water depth, (ii) substrate size, (iii) water depth and substrate size combined, and (iv) water depth, substrate and flow velocity in combination. Diurnal and nocturnal activities were recorded and analyzed throughout all experiments. Burbots of both length groups showed a significant preference for deeper water depths and large cobble substrate. Substrate type was found to be the dominant factor determining habitat preferences of L. lota when investigated in combination with water depth. In experiments combined with flow velocity, substrate and water depth were the most important factors determining burbot habitat preferences, and flow velocity of minor importance. In general, burbots were most active at night, while daytime activity was much lower. However, in all experimental approaches in the smaller length group the burbots displayed much higher day- and night-time activity than did the individuals in the larger length group.