Description

Abstract: A bioenergetics model was developed to simulate growth of both caged and open-pond Nile tilapia in a cage-cum-pond integrated culture system. The model incorporated six key variables affecting Nile tilapia growth in the cage-cum-pond integrated culture system: body size, water temperature, photoperiod, dissolved oxygen, unionized ammonia and food availability. Caged tilapia were given artificial feed, while growth of open-pond tilapia was dependent on uneaten artificial feed from the caged tilapia and natural foods derived from cage wastes. In the model, availability of natural foods was estimated by a relative feeding level parameter, which was a function of potential net primary productivity based on fish standing crop and the limiting nutrients in the ponds. The model was validated using growth data for both caged and open-pond tilapia in 28 ponds. The model described 96 and 85% of the variance in growth of caged and open-pond tilapia, respectively. Statistical analyses indicated significant agreements between predicted and observed values for both cage and open-pond systems. The model showed that the growth of open-pond tilapia was limited by phosphorus limiting primary production when the total number of tilapia stocked in cages was not greater than 200 fish pond-1, beyond which the limiting nutrient was phosphorus at the beginning of experiments and then shifted to nitrogen. The percentages of the culture period during which nitrogen limitation occurred increased from 0 to 84.4% with the increase of artificial feed inputs. The model revealed nitrogen from biological nitrogen fixation accounted for 44.2