Feeds and feeding strategies for Colossoma macropomum (Cuvier 1818) : fish growth as related to dietary protein

<em>Colossoma macropomum</em> is an indigenous fish species from the Amazon region. The amino acid profile of its body protein proved to be similar to that of other fish species. Soya meal and fish meal have, based on their amino acid profiles, a comparable protein quality. This hypothesis was confirmed in a feeding trial. As soya meal is less palatable than fish meal, more soya in the diet tends to decrease feed uptake and growth rate, but increases protein utilization efficiency. Growth of C. macropomum is fast and requires a dietary protein content of approximately 43%. Fish growing at maximal speed displayed a protein utilization efficiency of only 50% of the maximal possible efficiency. In ad libitum fed C macropomum 20 - 30% of the feed remains uneaten. In spite of this wasted feed, the feed uptake/weight gain ratio ranged between 0.57 and 0.71 with a high quality feed. Increasing the feeding frequency from one to five meals per day increased feed uptake and growth. Fish displayed a clear daily bio-rhythm with maximal feed uptake in the late afternoon. Lipid addition to the diet increased the protein utilization efficiency less than reported for salmon. An increased dietary protein content increased the body protein content and decreased the body lipid content. Adaptation of the size of the internal organs to the characteristics of the diet is possibly the cause that diet composition affects the body composition of fish. Accumulated data were analyzed by an empirical and an explanatory model. Both methods identified protein ration as the major variable determining fish growth. In describing the data, the average errors of both methods were similar. However, the empirical model produced more outlying values. It was concluded that the explanatory model with some minor improvements can be turned into a useful tool for research and practical management. Fast growth and a flexible body composition make C. macropomum a suitable study object for the development of improved fish growth models.