Abstract

Feeding experiments were performed at different light regimes to reveal consumption of plant and animal food (Elodea and shrimp) in the noble crayfish. The shrimps were consumed at a higher rate than Elodea. At summer temperature (17-18°C), daily consumption was respectively 10.5 and 6.5% of bodyweight on wet weight basis. Turnover rate considered as gut passage time was measured by use of dye and ranged 8.5-10.5 h. Daily mean weight gain for all individuals was 0.2% per day. Different light regimes had no significant effect either on quantitative food consumption, or on weight increase. Carbon and nitrogen contents of food and faeces indicated a higher assimilation efficiency of nitrogen (protein) compared to carbon. Based on the obtained feeding rates and density estimates in Lake Steinsfjorden, the contribution to the turnover of organic matter for crayfish (> 70 mm TL) was approximately 150 g organic matter per square m per year, or some 1000 tons for the 0-10 m depth stratum of the lake.

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