A model was formulated to estimate the carrying capacity (animal weight/area) and area of ponds in intensive culture of freshwater fish, managed with artificial feed. The model is based on a non-stationay mass balance of oxygen in the water, depending on the following parameters: water flow, ratio of oxygen concentration in the affluent and effluent pond, oxygen consumption per unit of animal weight, pond volume and water temperature. It was applied to the culture of rainbow trout.