To evaluate the potential to control red tides using the mass-cultured heterotrophic grazer, rotifer Brachionus plicatilis, the effects of environmental factors (water temperature and salinity) on physical activities (filtration and oxygen consumption rate) of B. plicatilis were estimated. Experiments were conducted at different water temperatures (15, 20, 25, 30 and 35°C) and salinities (20, 25, 30, 35 and 40 PSU), in 25 different combinations (5 temperatures × 5 salinities). Results showed that water temperature and salinity had significant effects on the filtration rate of B. plicatilis (F=41.66, P<0.05). The results of multiple regression analysis yielded the following functional dependence of filtration rate (F) on water temperature (T) and salinity (S): F=-1.658+0.917 T+0.63S (R2=0.769, P<0.001). The highest filtration rate (4.23 ±0.74 μl rot-1 h-1) was obtained at 30°C and salinity 35 PSU, and the lowest one (0.869 ±0.13 μl rot-1 h-1) was observed at 15°C and salinity 20 PSU. Both water temperature and salinity had significant effects on the oxygen consumption rate of B. plicatilis (F=34.08, P<0.05). The results of multiple regression analysis yielded the following functional dependence of oxygen consumption rate (O) on water temperature (T) and salinity (S): O=-3.133+0.165T+0.81S (R2=0.938, P<0.001). The highest oxygen consumption rate (5.38 ±0.66 ng rot-1 h-1) was observed at 35°C and salinity 40 PSU, and the lowest one (1.01 ±0.15 ng rot-1 h-1) was observed at 15°C and salinity 20 PSU. Results from this present study indicated that the filtration and oxygen consumption rate of the rotifer were significantly influenced by the water temperature and salinity. The utilization of rotifer for red tide control has to consider the influence of environmental factors.
