The digestibility of nutrients in six semi-purified rations containing variable levels of protein, cellulose and starch by channel catfish in troughs was evaluated by using chromium oxide as an inert reference in the feeds. Excreta were collected using an indirect trough collection method and a direct intestinal collection method. Digestibility coefficients determined on excreta collected in troughs were higher than coefficients determined from excreta collected from the intestine. There was no significant difference in protein Or fat digestibility from the six rations when the trough collection of excreta method was used. In the intestinal collection method, excreta were collected, separately, from four areas of the digestive tract, namely, the stomach, upper intestine, lower intestine and rectum. The absorption of protein in twoyear old channel catfish occurred the length of the intestine up to and possibly including the rectum. There was a significant difference in protein digestibility among the six rations for collection of excreta from the rectal area. A higher percentage of protein was digested in rations containing 40% protein than in those containing 20% protein. Starch did not seem to affect protein digestibility but cellulose did. Protein digestibility coefficients ranged from 72 to 93%.
