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SynopsisUse of a radiographic technique enabled the study of prey selection and individual specialization in Arctic chary, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions . Both naive and experienced fish (mean weight 475 g, mean length 34 .9 cm), selected the smallest individuals when offered juvenile charr (6-16 cm) as prey. The selected prey were, on average, 22% of the predator length . Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised : cannibals, pellet eaters and non-feeding fish .

There are three main methods used in the study of feeding behaviour and food consumption in captive populations of fish. These are direct observation, the recording of feeding activity using 'on-demand' feeders, and the quantitative determination of gastrointestinal content using a non-invasive 'labelled feed' technique. Observational techniques have been widely used in studies of foraging behaviour and feeding responses, but these methods are usually confined to the study of fish held in small groups. 'Labelled feed' techniques are well suited to the monitoring of feed intake of individual fish held in large groups, but cannot be used for the continuous monitoring of feeding behaviour. They are, therefore, not particularly suitable for the collection of information about short-term changes in feeding rhythms, or possible die1 changes in feeding activity. Studies of feeding activity may best be carried out using computer-operated 'on-demand' feeding systems, but the data collected using these systems give no information about individual feed consumption. Examples are presented showing how data collected using the three methods can be used to provide insights into how various abiotic and biotic factors influence fish feeding. K E Y WORDS: demand feeders, feeding behaviour, food intake, growth studies, X-radiography ~ ~ ~~~