Assessing the Status of Rotifer Mass Cultures

Abstract

AbstractRotifers are widely used as live larval feed in aquaculture. The stability of rotifer mass cultures, however, remains a critical unresolved problem. It would be useful to develop indicators that can assess the status of rotifer mass cultures and serve as an early warning of trouble. Indicators should be sensitive, easy to measure and have quick response time. Two indicators have been developed that fulfill these criteria: swimming activity and egg ratio (eggs per female). A swimming activity test is described based on the measurement of rotifer swimming over a grid. Results are obtained in minutes and are sensitive indicators of pH, un‐ionized ammonia, starvation and temperature stress in the mass culture. For un‐ionized ammonia, swimming activity is about nine times more sensitive than an LC50 test, and maximum response occurs within ten minutes. Egg ratio is also a sensitive indicator of physiological stress, but there is a 18‐24 h time lag between exposure to stress and a change in egg ratio. Egg ratios during log phase of population growth ranged from 0.5‐1.2 and 0.13‐0.5 during stationary phase. When egg ratio fell below approximately 0.13, rotifer populations declined. Monitoring of swimming activity and egg ratios should make it easier for aquaculturists to keep their rotifer cultures productive and stable.