The oxygen concentration in a tank of water is described by this model. There is an inflow of oxygen into and an outflow out of the tank. The oxygen is dissolved in water, and the flow of water is described by the flow rate. The inflow as well as the oxygen concentration is affected by the solubility of oxygen in water. Temperature affects the oxygen solubility, and this temperature-dependence is described by a polynomic regression obtained from empirical data.
The outflow of oxygen depends on the concentration of oxygen in the tank as well as the flow rate.
A fish respires in the tank. The overall respiration rate is affected by the temperature (the dependence is described by a polynomic model obtained from empirical data), the weight of the fish and the oxygen level in the tank. A threshold value of 1,8 cc/L (obtained from empirical data) is the oxygen level that leads to the maximum respiration rate and the oxygen dependence factor is 1 at and above the threshold value. Below the threshold oxygen level, the oxygen dependence factor is between 0 and 1. The oxygen level below the threshold value affects the oxygen dependence in a linear fashion.