Growth performance of the rotifers Brachionus plicatilis, B. ‘Nevada’ and B. ‘Cayman’ under different food concentrations

Numerical response experiments were conducted using three strains of the Brachionus plicatilis species complex. They are commonly used in aquaculture, and could also coexist in nature although this has not been studied yet. Brachionus plicatilis sensu stricto (s.s.), B. ‘Cayman’ and B. ‘Nevada’ were cultured at different concentrations of Nannochloropsis oculata (0-40 mg C l^− 1). Growth rate, egg female ratio (EF), fecundity and percentage of ovigerous females were determined at each food concentration. From the growth rate and EF, the egg development time and mortality rate were estimated using the Paloheimo equation. Monod curves with a threshold for zero growth described the relationship between growth rate and food concentration. The three strains had different growth rates at low (< 0.04 mg C l^− 1) and high (> 5.0 mg C l^− 1) food concentrations, but were similar at intermediate food levels. B. ‘Cayman’ had the highest maximum growth rate (1.57 ± 0.07 d^− 1), whereas B. plicatilis s.s. had the less negative minimum growth rate and the highest maximum EF (0.96 ± 0.02 eggs ind^− 1). These differences were attributed to the lowest egg development time of B. ‘Cayman’ (5.95 ± 0.24 h) and the higher starvation resistance of B. plicatilis s.s. (84 ± 12 h), respectively. B. ‘Nevada’ was the inferior competitor at high and low food concentrations due to the higher investment in body growth rather than reproduction. The outcome of competition in hatcheries is predicted to favor B. ‘Cayman’ under high food concentrations, whereas the three species may coexist under moderate food limitation.