Automatic control of growth and density in rotifer cultures

Abstract

A system for automatic control of the growth and density of rotifer cultures is presented and tested. The system computes feeding rates based on a setpoint for rotifer density, and provides a fast growth period followed by rapid stabilization of the rotifer density. At the same time, overfeeding is prevented, thereby reducing the risk of culture crashes. Feeding rates are automatically computed based on measurements of the culture’s density and egg rate, and internal setpoints for growth rate and egg rate. The controller is tested and tuned against a mathematical model of a rotifer culture before being applied to four experimental cultures. The experimental results show densities in all tanks increasing from 60 to 90 ml −1 to the setpoint densities of 500 and 1000 ml −1 in 5–7 days, after insignificant growth on the first day. Gross growth rates slowed down considerably towards the end of the experiment, as the controller reduced feed rations in order to stabilize densities. The cultures were stabilizing at higher densities compared to their setpoints, while there was no such bias in the observed egg rates. This indicates that a part of the controller algorithm needs further tuning. The approach to the setpoint densities was fast, and within the experimental period there were no indications of oscillations beyond those caused by daily dilution.