Modelling The Fate And Effects Of Feed-Based Pollutants In Intensive Fish Pond Systems

Abstract

Fish pond processes and interactions are quite complex and models have been developed to aid their understanding. Most existing models, however, were designed for foreign species and environment. Inthis study, development of a model for studying the fate and effect of feed-based pollutants in intensive African catfish ponds was undertaken.The model was formulated from theoretical relationships for intensive catfish culture, and coded into computer program software with Microsoft® Visual C# (C-sharp). The model was designed to predict general pond dynamics; identify causes and suggest remedial actions for impaired systems; predict feed wastage and economics of production; and track the fate of water quality parameters which are not readily measured. The model was verified, calibratedusing published experimental data from a 5m × 4m × 1.2m fishpond, and validated using observed data from a monitored 50m × 10m × 1m fish farm, stocked at 10 fish/m2 in Nsukka, Enugu State, Nigeria. Sensitivity analysis was carried out on the 1 model parameters at ± 20% input parameter change and general guidelines for parameter estimation were obtained. Model experimentation was carried out on different pond management scenarios with stocking densities of 7 fish/m2, 14 fish/m2, 21 fish/m2, 28 fish/m2 and 35 fish/m2. The model, termed Aquacultural Simulation Management Tool (AQUASMAT)gave a close prediction of observed data, showing reasonable performance and adequacy of system representation. Regression analysis of validation results gave strong correlations between predicted and observed data with R2 of 0.96 for TAN, 0.61 for temperature, 0.97 for NO3 and 0.99 for fish weight. Model adequacy was tested with relative bias (rB) giving results of 0.014, -0.159, 0.039, -0.104; and the F-test giving results of 0.740, 0.877, 0.887 and 0.736, respectively for temperature, DO, TAN and fish weight. These results fall within acceptable range for each test.The model is sensitive to parameters such as temperature, pond size, feed and stocking density; ±20% change in feed input directly affected accumulation of NH3 - and metabolic waste; 20% increase in stocking density caused a 22% reduction in DO, 87% increase in NH3 - and 24% decrease in fish weight; 20% increase in temperature directly affected NH3 - with 45.80% increase and 89% decrease in fish weight, while 20% decrease in temperature caused 25% decrease in fish growth and 50% decrease in NH3 -. Accurate estimation of these parameters is required for optimal performance of the model. Model experimentation results showed DO and TAN were within tolerable water quality limits only for stocking densities of 7 fish/m2, 14 fish/m2 and 21fish/m2. The economic viability of the modeled scenarios showed a profit of N1,100:00, N1,681:00, N1,575:00, andN820:00 for 7 fish/m2, 14 fish/m2, 21 fish/m2

and 28 fish/m2, respectively, and a loss of N1501:00 for 35 fish/m2, showing an optimum production at stocking density of 21 fish/m2.