Food nutrient dynamics model for semi-intensive pond aquaculture | |
| Author | Li, Lanhai |
| Call Number | AIT Diss. no.AS-97-07 |
| Subject(s) | Pond aquaculture Fishes--Feeding and feeds |
| Note | A dissertation submitted in partial fislfillment of the requirement for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | A nutrient dynamic model for pond aquaculture has been developed as a tool to explain food nutrient dynamics in a fertilized pond and to determine the food nutrient requirement for supplementary feeds for tilapia growth. Based on the dynamic process of food nutrients in a fertilized pond, causal relationships linking the pond ecosystem structure to food nutrient behavior have been recognized, and a System Dynamics model is created using STELLA software. The model is divided into five sectors: food nutrient sector (including three stocks: autotrophic food nutrient, heterotrophic food nutrient and organic particulate from organic fertilizer), fish growth sector (including two stocks: fish biomass and fish number), elementary nutrient sector (including two limiting elementary nutrients: inorganic nitrogen and phosphorus), dissolved oxygen sector and exogenous factor sector. The exogenous factors include solar radiation, temperature, fertilization, supplementary feeding and fish stocking. Fertilization, supplementary feeding and fish stocking are the exogenous factors related to management and are designed as decision-making points for improving the dynamic behavior of food nutrients. After the model structural validation, model behavioral tests and policy implication tests are conducted. The model behavioral tests indicate that model behavior agreed well with the reference. patterns from literature. The sensitivity analysis of the model behavior shows that the parameters related to autotrophic food nutrient growth rate, elementary nutrient sources and exogenous factors are more sensitive numerically than other parameters. Selecting primary producer’s Species with high growth performance and ponds with high initial elementary nutrient amount in sediments can increase food nutrient productivity and fish growth rate. Fertilization and supplementary feeding can significantly improve food nutrient availability and compensate natural food nutrient deficiency for further fish growth. Policy implication tests testify that an increase in fertilization rates can increase food nutrient supply and mean fish weight until a safe loading level reached, and that fertilization with a balanced proportion of nitrogen to phOSphorus is suggested. Supplementary feeding in a fertilized pond can produce significantly higher fish yield. The model can quantify the desired loading rates of fertilizers and supplementary feeds under the desired nitrogen and phosphorus concentrations. The confidence of the model is further built up by two field experiments from ODA project. The experiments were designed to determine the nutritional limiting factors for fish growth both in only chemically fertilized ponds and in fertilized ponds with supplementary feeding. The model is fed by initial values of the stocks, field data of both meteorological variables and management activities. The simulated results show that food nutrient supply and mean fish weight increase with an increase in nitrogen and phosphorus loading rates, and that significantly higher mean fish weight is obtained from fertilization accompanied with supplementary feeding. The simulated results also reveal that the protein and vitamin supplements are necessary for increasing fish yield. The simulated data are compared with observed and interpolated data, and analyzed using Theil statistics. The results indicate that the simulated fish biomass has a good correspondence to observed data. Although some variables have a high root-mean-square percent error, the decomposition of the error sources shows that the error is mainly caused by environmental noise and randomness. The model is able to capture the essential food nutrient dynamics and reproduce the historical behavior. |
| Year | 1997 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Aquatic Systems(AS) |
| Chairperson(s) | Yakupitiyage, Amararatne; |
| Examination Committee(s) | Dahl-Madsen, Karl Iver;Lin, C. Kwei,;Edwards, Peter; |
| Scholarship Donor(s) | Overseas Development Administration (ODA) London; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1997 |