Methodical studies on digestion in trout. 1. Reliability of digestion coefficients in relation to methods for faeces collection

Two methods of faeces collection were compared when studying digestion in trout (78–200 g individual weight; 12–15°C): (a) Faeces stripped from the lower intestine; (b) faecal pellets filtered continuously from water using an automated faeces collector. This apparatus consisted of a cylindrical tank with a funnel shaped bottom, from which the effluent water was drained over a rotating cloth filter, separating the faecal pellets immediately from water. The digestion coefficients for energy and protein of a commercial feed and an experimental diet were determined applying both methods of faeces collection. Digestion coefficients for protein of the experimentally composed diet were 1–2·3% higher for the filtered faeces than for the stripped faeces (88·6–87·3%). The protein digestion coefficients for the commercial feed were about 5% higher when faeces were sampled by continued filtration. Results obtained with the stripping method averaged 79·5%. The energy digestion coefficients followed a similar trend. It was concluded that the stripping method gives more reliable digestion coefficients.