Abstract

The objective of this investigation was to study the nutrient release from the noble crayfish (Astacus astacus) fed two different diets in aquaria experiments. They were fed with either alga (Chara globularis) and rudd (Scardinius erythrophthalmus) or a commercial diet formulated for crayfish aquaculture. Five individuals between 6.5 and 9.0 centimetres were stocked in each of 20 aquaria containing 40 L of water. During the experiment, water samples were taken every five days for the analyses of ammonium, nitrite+nitrate and phosphate. The ammonia concentration in the water was higher when fed fish and alga compared to a pelleted feed. The same tendency was true also for nitrite+nitrate concentration although not so pronounced. The phosphate concentration in the water differed less between the two diets. Ammonium and phosphate concentration in the water decreased in the presence of sediment while nitrate+nitrite concentration increased. The increase in concentration of inorganic nitrogen in the water per biomass was smaller when fed pellets and especially in aquaria with limestone sediment present. The growth increment and moulting frequency were noted. The amount of excreted inorganic and phosphorus per kg biomass and biomass increase were calculated.

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