Apparent digestibility coefficients (ADCs) of amino acids, crude protein, gross energy, and dry matter of canola meal, corn gluten feed, fish offal meal, shrimp and fish offal meal, poultry by‐product meal, and hydrolyzed feather meal were determined for channel catfish, Ictalurus punctatus. Experimental diets contained 30% test ingredient, 69.5% casein‐based reference diet, and 0.5% chromic oxide. Groups of 20 fish (102.45 g) were fed the experimental diets twice a day at 3.5% body weight. Fecal samples were collected in triplicate daily at 0000 h and 0600 h after settlement into collection devices. Shrimp and fish offal meal and corn gluten feed presented significantly lower (P < 0.05) ADC for dry matter (59.5 and 39.3%) suggesting their low value as feedstuffs for catfish feeds. Although ADC values for crude protein were above 80% for all the test ingredients, amino acid digestibility varied significantly, except for histidine whose ADC remained constant regardless of the protein source. Lysine was the first limiting amino acid in most of the test ingredients, except in fish offal meal and poultry by‐product meal. Among the protein sources tested, only fish offal meal and poultry by‐product meal met channel catfish amino acid requirements for a 28% digestible protein grow‐out diet.

Channel catfish, a major freshwater aquaculture species in the US, is also farmed in Southern Brazil. However, apparent digestibility coefficients (ADC) of nutrients in commercial feeds available in Brazil for the species are not known. This study aimed at optimizing a methodology for fecal collection and determination of apparent nutrient digestibility for catfish. Pilot trials were carried out to establish gastrointestinal transit, fish density, and time interval between fecal collections. Gastrointestinal transit of dry feed for catfish varied from 11h30 to 10h30 for 100 and 172-g fish, respectively. Average dry weight of feces produced along a six day period by 99-g fish was 0.54 g, regardless of stocking density (10, 15 or 20 fish per 98-L cage; p > 0.05). Described methodology allowed the collection of average 10.80 g feces per tank (dry weight) in three days. Feces collected at 1, 6 or 12 h had increased protein digestibility from 1 to 12 h, that is, there was increased protein leaching as the time of feces exposure to water increased. Fecal collection was optimized at 20 fish per tank and 6 h interval between collections. ADC of protein, energy, and dry matter of four commercial feeds for catfish using the indirect method with the addition of 0.5% of Cr 2 O 3 as an inert maker was also evaluated. Crude protein contents of commercial feeds matched manufacturer's specifications but did not yielded the 28% digestible protein required for adequate channel catfish growth. The digestible protein of commercial feeds ranged from 23.3% to 25.6% and digestible energy ranged from 1177 to 1249 kJ 100 g -1 feed. It is instrumental measuring nutrient digestibility when evaluating commercial feeds. Key words: nutrient availability, fish nutrition, siluriform fish, channel catfish Validação de um método para medir a digestibilidade de nutrientes e avaliação de rações comerciais para catfish RESUMO: O catfish americano, espécie aquícola importante nos Estados Unidos, também é produzido no sul do Brasil. Entretanto, a digestibilidade dos nutrientes das rações disponíveis no Brazil não é conhecida. Nesse estudo otimizou-se a coleta de fezes e a determinação do coeficiente de digestibilidade aparente (CDA) para a espécie. Ensaios pilotos foram conduzidos para determinação do tempo de passagem do alimento no trato digestório, densidade dos peixes e intervalo entre coletas de fezes. O tempo de passagem variou de 11h30 a 10h30 em peixes com peso médio de 100 e 172 g, respectivamente. O peso médio (base seca) das fezes produzidas por peixes (peso médio 99 g), em seis dias, foi 0.54 g, independentemente de a densidade ser 10, 15 ou 20 peixes por gaiola (p > 0.05). Com esta metodologia foi possível coletar 10.80 g de fezes (base seca) por tanque em três dias. A digestibilidade da proteína aumentou com intervalos de coleta de fezes de 1, 6 e 12 h, indicando aumento na lixiviação deste nutriente à medida que aumentou o tempo de exposição das fezes à água. A coleta de fezes foi otimizada com 20 peixes por tanque e com 6 h ...