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RESEARCH PRODUCT

Influence of the concentration of oxygen on the swimming path of Brachionus plicatilis (Rotifera)

subject

description

Brachionus plicatilis females were maintained for > 24 hours in water where the concentration of oxygen was precisely controlled (spherical flasks with ≥ 6 mg 1−1 or < 0.5 mg 1−1; food = dead Tetraselmis sp.). Each female was randomly taken from one flask and quickly placed in an observation chamber containing the same experimental conditions. The swimming path was videotaped (5 minutes); then the size of the female was measured. The tape was analyzed by automatic tracking (25 x, y coordinates of the center of the animal, in a 512 × 512 pixels space). The swimming path was analyzed for ~45 females in both treatments. The speed (mm s−1 body length−1) was calculated for all trajectories, or only for those segments where females swam in a horizontal plane. This relative speed significantly decreased when the concentration of oxygen was very low. There was a negative correlation between the linear speed and the angular speed. The spatial sinuosity (‘S’ of Bovet & Benhamou, 1988) was calculated. The trajectories were significantly more sinuous when the concentration of oxygen was very low. These results could explain the accumulation of some rotifers in the oxycline; rotifers may spend more time in very low concentrations of oxygen by slowing and by turning more.