Behavior and reproduction of the rotifer Brachionus plicatilis species complex under different light wavelengths and intensities

We investigated the influence of light on phototactic behavior and reproduction in two species of rotifer from the Brachionus plicatilis species complex (B. plicatilis sensu stricto (s. s.) and Brachionus manjavacas). This was done to understand how light effects these species so that we might use this knowledge to establish a more efficient aquaculture protocol. We used four different light wavelengths (white, with peaks at 460 and 570 nm; blue at 470 nm; green at 525 nm; and red at 660 nm) and four intensities (i.e., 0.5-30.0 W/m(2)). Using micro-spectrophotometry we determined that eyespots of these two Brachionus species absorbed blue and green light 5.5 times more than red light. B. plicatilis s. s. showed positive phototaxis under white, blue, and green light at lower light intensities, but no phototaxis under red light at all intensities (0.5, 6.2, 15.0, and 30.0 W/m(2)). Similar patterns of phototaxis were observed in B. manjavacas and did not differ among mictic, amictic females, and male rotifers. Population growth rate of B. plicatilis s. s. under dark condition was 1.1-1.2 times higher than that under white light condition. No significant differences were observed in population growth rate at 3.8 and 6.2 W/m(2) at all light wavelengths. On the other hand, population growth rates at 0.5 and 1.6 W/m(2) were the lowest under blue light. According to these results, both wavelength and intensity of light affect the population growth of rotifers, which in turn may be influenced by the rotifers' wavelength-dependent phototaxis.