Growth and gastrointestinal indices in Nile tilapia fed with different diets/Crescimento e indices gastrintestinais de tilapia do Nilo alimentadas com diferentes dietas

The adequate diet of Nile tilapia in their growth early stages is fundamental to the success of culture subsequent stages. The goal of the present work was to evaluate the Nile tilapia growth fed with different diets, and to morphometrically characterized the gastrointestinal tract of this species. The treatments consisted of three diets: ([D.sub.1]) natural food, ([D.sub.2]), commercial feed and ([D.sub.3]) commercial feed + natural food. In the qualitative phytoplankton analysis, there was greater representation of the genus Chlorella, while zooplankton community analysis revealed greater number of Brachionus rotifer. Growth and survival in [D.sub.2] and [D.sub.3] did not reveal differences (p > 0.05), while in [D.sub.1], the results were significantly lower (p < 0.05). The gastro-somatic and entero-somatic indices, and the intestinal quotient revealed higher values when only natural food was available. Nile tilapia reached best zootechnical performance when commercial feed was included in the diet. The intake of natural and/or artificial food is related to the growth and development of the gastrointestinal indices, emphasizing that these indicators can be altered by the type of feeding. Keywords: Oreochromis, diets, natural food, plankton, digestive tract. A dieta adequada de tilapia do Nilo em suas fases iniciais de crescimento e fundamental para o sucesso das etapas subsequentes do cultivo. O objetivo do presente trabalho foi avaliar o crescimento de tilapias do Nilo alimentadas com diferentes dietas e caracterizar morfometricamente o aparelho gastrintestinal da especie. Os tratamentos constaram de tres dietas: ([D.sub.1]) alimento natural, ([D.sub.2]) racao comercial e ([D.sub.3]) racao comercial + alimento natural. Na analise qualitativa do fitoplancton, observou-se maior representacao do genero Chlorella enquanto a analise da comunidade zooplanctonica revelou maior numero de rotiferos do genero Brachionus. O crescimento e a sobrevivencia em [D.sub.2] e [D.sub.3] nao apresentaram diferencas (p > 0.05), enquanto em [D.sub.1] os resultados foram significativamente inferiores (p < 0.05). Os indices gastrossomaticos, enterossomaticos e o quociente intestinal apresentaram, de uma maneira geral, valores superiores nos tratamentos que utilizaram alimento natural na dieta. Tilapia do Nilo alcancou melhor desempenho zootecnico quando a racao comercial foi incluida na dieta. A ingestao do alimento natural e/ou artificial esta relacionada com o desenvolvimento