| Summary: | The aims of this thesis are to determine the role of burbot in the freshwater ecosystem and clarify how the feeding biology and behaviour have been affected by the profundal life style of burbot. The gastric evacuation rates of burbot fed single fish meals were measured under various experimental conditions. The gastric evacuation rates of the burbot were affected by water temperature and meal size in the temperature range of l.3-12.6°C, as has earlier been observed about several fish species. However, the stomach emptying rates were low compared to other freshwater fish species. As stomach emptying is prolonged, the stomach can act as a reserve of food during the periods of low prey availability. In the experimental conditions, the estimated optimum temperature for food intake (g g⁻¹) was 13.6°C. Food consumption estimates suggest that burbot are potential competitors for food with other piscivorous fish. Seasonal changes in burbot's diet may, however, decrease their impact on prey fish species. Indeed, the profundal life style provides the adaptation to nearly zero illumination and low temperatures. Ambush feeding behaviour with low metabolic rates are characteristic of the burbot, a major predator in various freshwaters. The burbot has adapted to use dark periods of the day for activity during most of the year. Food composition and stomach fullness data suggest that burbot are periodic and opportunistic feeders, that have adapted to prey under unpredictable food conditions.
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