This article introduces a application of modeling theory and agent-based simulation to build a model simulating how the propagation of catfish (pangasius hypophthalnus - Ca Tra, in particular) diseases works under physical, chemical, and bacterial conditions of fishponds and water flow in some areas in Mekong Delta, Vietnam. In particular, the model is built focusing on the disease of white spots on the internal organs of catfish in a typical district-level administrative unit in the Mekong Delta (Phu Tan district, An Giang province). The model helps us to observe how environmental conditions affect the way the pathogen (bacteria) propagate along the river, from the river to fishponds and vice versa by adjusting the input arguments. The authors are also able to monitor how the disease propagates among individual fish in a single fishpond. The objective is to predict the infectious or healthy state of fishponds. The model's input arguments such as originally infectious state, temperature, pH value, and so on can be adjusted, i.e. different environmental conditions, to obtain different results.