Locomotory behaviour of euryhaline rotifer Brachionus rotundiformis: The potential influence of probiotics on swimming pattern and speed

We evaluated the effect of probiotics on the growth and culture condition of rotifer in medium-sized culture tanks. The influence of probiotics on the changes in swimming patterns, velocity and sinuosity indices of rotifer was also examined. The rotifers (Brachionus rotundiformis) were cultured for 14 days in nine polycarbonate tanks containing seawater which were divided into three groups: a control group (Chlorella product) and two treatment groups: Chlorella + Probiotic I and Chlorella + Probiotic II. The rotifer population and the water quality parameters were monitored daily. To evaluate the locomotory behaviour of the rotifer, a sub-sample containing rotifers was obtained from each treatment and placed on a glass-bottomed dish. A high-speed camera mounted on a stereo microscope was used to record the rotifer movement. The footage was then analysed using motion analysis software to establish the swimming velocity, swimming pattern and sinuosity indices of the rotifers. Co-feeding rotifer on microalgae and probiotics resulted in a higher rotifer growth rate (0.51 ± 0.03) and decreased concentration of unionized ammonia (0.14 ± 0.02 mg L⁻¹). In addition, the probiotic-fed rotifers had 1.59 times higher average swimming velocity (0.97 ± 0.11 mm s⁻¹) and more straight swimming pattern compared to rotifers that fed on microalgae alone whose velocity was slow (0.61 ± 0.14 mm s⁻¹) and more sinuous. From these data, we can postulate that probiotics have the potential to attenuate rotifer culture conditions by decreasing ammonia concentration as well as influence rotifer swimming behaviour which could affect rotifer reproduction and the quality of fish larvae in aquaculture systems.