Effect of dietary essential amino acids addition on digestive enzime secretion in silver catfish Rhamdia quelen

Studies carried out with variation of protein concentration in the fish feed have shown an increase in the activity of alkaline proteases, acid proteases, trypsin and chimotrypsin from the digestive tract of silver catfish (Rhamdia quelen). These facts suggest that products released by digestion in the lumen of this tract can influenced the synthesis and secretion of digestive enzymes. The secretion of these enzymes by the pancreas in vertebrate responses to neural and humoral influences. In the present study, four concentration (0, 3, 6 and 12%) of an amino acid mix (threonine, phenylalanine, leucine, valine, arginine and thryptophan, in equal amounts) were tested in isocaloric (3500 kcal of digestible energy kg-1 of feed) and isoproteic (20% of protein) diets on juveniles of silver catfish. It was used 10 specimens per treatment stocked in a water recirculation system, with controlled and constant temperature. The fish submitted to the treatments presented alkaline activity in the anterior region of the gut, responding to the different levels of amino acid in the feed. Although there was alkaline proteases activity in the liver, the amylase activity of the liver and anterior gut was not observed. Key words: fish, jundia, diet, enzymes, biochemistry, hematology. Em estudos realizados com variacao no teor de proteina na racao para peixes, foi demonstrado o aumento das atividades de protease alcalina, protease acida, tripsina e quimiotripsina do trato digestorio de jundia (Rhamdia quelen). Esses fatos sugerem que produtos liberados pela digestao na luz desse trato podem influenciar a sintese e a secrecao de enzimas digestivas. A secrecao destas enzimas pelo pancreas, em vertebrados, responde a influencia neural e humoral. No presente trabalho, foram testadas quatro concentracoes (0, 3, 6 e 12%) de uma mistura de aminoacidos (treonina, fenilalanina, leucina, valina, arginina e triptofano em iguais proporcoes) em dietas isocaloricas contendo 3.500 kcal de energia digestivel [kg.sup.-1] de racao, e dietas isoproteicas contendo 20% de proteina, em juvenis de jundia. Foram utilizados dez animais por tratamento, sendo os peixes estocados num sistema fechado com recirculacao de agua e temperatura controlada. Os peixes submetidos a estes tratamentos apresentaram atividade da protease alcalina na regiao anterior do intestino, responsiva aos diferentes niveis aminoacidos da alimentacao. Todavia, as atividades protease alcalina do figado e amilase do figado e intestin