Description

Abstract: A bioenergetics growth model for Nile tilapia in fertilized ponds, which linked Nile tilapia

growth with limiting nutrients in pond water, was developed. The model incorporated six key variables affecting Nile tilapia growth in fertilized ponds: body size, water temperature, photoperiod, dissolved oxygen, unionized ammonia and food availability. In the model, food availability was estimated by a relative feeding level parameter, which was a function of potential net primary productivity based on limiting nutrients, and standing crop of Nile tilapia. The model was validated using growth data of Nile tilapia in 30 fertilized ponds, and successfully detected growth variations among ponds receiving the same nitrogen and phosphorus inputs. The model described 76% of the variance in growth in these ponds, and the relationship between predicted and observed growth rates had a slope of 0.93 and an intercept of 11.51, not significantly different from 1 and 0, respectively. The model indicated that the growth variations were caused by carbon limiting primary production during 55-99% of the culture period. Sensitivity analysis indicated that the parameters related to net energy from feeding were more sensitive than those related to fasting catabolism, and that the growth was most sensitive to photoperiod and then food availability when DO was above its critical limit (1.0 mg l-1), but was most sensitive to DO when it was below the critical limit. Tilapia growth was more sensitive to DO than UIA. Initial tilapia size was the least sensitive variable when UIA was above the critical limit in the model. Compared with previous models, this study provides a more reasonable and accurate way to estimate relative feeding level ( f ) based on fish standing crop and potential net primary productivity derived by a limiting nutrient.