Abstract
The bioenergetics fish growth model of Nile Tilapia (Oreochromis niloticus) cultured in the cages in wastewater
oxidation pond is presented. The oxidation pond is located in the very successful project area “The Leam Phak Bia
Environmental Study Research and Development Project under Royal Initiatives Petchaburi Province” in Thailand.
There are five oxidation ponds connected in series in the research area. The measurement of Nile tilapia growth is
taken in the third pond in which the water quality is in the effluent standard. The water quality and fish weight are
measured in each month for one year period. The fish growth model in the form of ordinary differential equation is
introduced to understand the behavior of fish growth due to various environmental factors which are dissolved
oxygen demand (DO), water temperature, concentration of plankton, ammonia and biochemical oxygen demand
(BOD). In this presented model, we have introduced a new form of food assimilation efficiency as a function of fish
weight. It is found that the predicted fish weight obtained from the model is in good agreement with the
measurements. Also, this presented model can be applied to predict the fish weight in a wastewater stabilization pond
when environmental factors have been changed.