Quantitative and qualitative aspects of energy acquisition of the cichlid fish Oreochromis niloticus L.

Abstract

A unified theory of fish growth and feed intake was proposed with the aid of a conceptual growth model. Feeding experiments were performed with individuals and groups of Oreochromis niloticus (L) (2-50g in weight) using diets with differed biochemical composition. The functional relationship between growth and feed intake was found to be linear, irrespective to the growth indices is used as the dependent variable. The protein and energy requirement of O. niloticus was quantified and maximum requirements of 2 - I2g fish was approximately 22g protein kg**BW day** or 990 kJ-* kg**BW day**. In terms of mammalian physiological fuel values. The requirements of fish of 18 - 50g weight range was approximately 12g protein kg** BW day*’ with a corresponding energy intake of 650 kJ’’ kg*’BW day*’ for the maximum growth. Feeding fish above those limits resulted in a slight retardation of growth. The maintenance requirements were computed with the regression curves of growth and feed intake and found to be vary depending upon the equation used. The digestibility coefficients of protein, lipid and carbohydrates ware established to be as high as 90%, and the coefficients did not change over the weight range of the experimental fish. The optimum non-protein and protein energy ratio (NPE/PE) for O. niloticus was 1.72 and NPE was further analysed into lipid (LE) and carbohydrate energy (CE). It was found that the LE/CE ratio for O. niloticus is 2.25 in terms of mammalian physiological fuel values. A development of the conceptual growth modal for predictive growth modelling was discussed.