Bioenergetic modelling of effects of fertilization, stocking density, and spawning on growth of the Nile tilapia, Oreochromis niloticus (L.)

A bioenergetic growth model was developed to examine the integrated effects of fertilization, stocking density, and spawning on the growth of tiiapia, Oreochromis niloticus (L.), in pond aquaculture. The analyses showed that growth rates increase with higher levels of organic ferlilization up to 5(HJkg/ha/week. Growth rates increased with added food rations in ponds, reaching a maximum growth of 2-07g/day at about 44-48 days after stocking. Fish growth rates decreased with increased levels of stocking density. The stocking density for optimal growth is 1 fish/m"; the optimal density for total harvesting weight and fish size is 2 fish/m". Model sensitivity analysis indicated that tiiapia growth is most sensitive to catabolism (metabolism) and anabolism (synthesis) coefficients, both of which are geometrically related to the fish body weight. Food assimilation efficiency (b) and the food consumption coefficient (h) have a modest effect on fish growth. Spawning in grow-out ponds can have a major effect on fish growth. Introduction Pond richness, stocking density, and spawning can significantly influence fish growth in ponds. The levels and relative effects ofeachofthe factors on the rates offish growth in ponds are difficult to discern since many of these effects are dependent and interactive. In lilapia culture, this problem can be particularly significant since ponds are stocked at a density close to or beyond the pond carrying capacity. At these levels of stocking density, tiiapia can sexually mature at an early age and leads to a condition called 'stunting', which frequently results in excessive recruitment, and reduces growth and yields of harvestable-size fish. The objective of this study is to develop a bioenergetic model to evaluate the relative effects of fertilization, stocking density, and spawning on tiiapia growth, and to study the optimal conditions of tiiapia growth and yield under different cultural conditions. Bioenergetic models A bioenergetic model was developed using the Ursin (1967) model, including factors such as fish size, rations, levels of fertilization, stocking density, and spawning. Correspondence: K. M. Liu, Center for Great Lakes and Aquatic Sciences, University of Michigan, Ann Arbor. Michigan 48109, USA.