Population growth of Euchlanis dilatata (Rotifera): Combined effects of methyl parathion and food (Chlorella vulgaris)

In the present work, the combined impact of four concentrations (0, 0.0625, 0.125, and 0.25 mg/L) of methyl parathion and three densities (0.5 x 10(6) , 1.0 x 10(6), and 2.0 x 10(6) cells/mL) of the green alga Chlorella vulgar is on the population growth of Euchlanis dilatata was studied. In general, regardless of the food level, an increase in the concentration of methyl pa rathion resulted in a significant reduction of the maximal population densi ty and rate of population increase. The population growth rate in the contr ols ranged from 0.248 to 0.298; rates were lower in the presence of the pes ticide. At any toxicant concentration, rotifers fed higher algal density sh owed significantly higher population growth compared with those at lower fo od levels. An interaction between toxicant and food level was evident on th e population growth of E. dilatata. Results have been discussed in light of the protective role of algal density on the toxic effects of insecticides on rotifers and the differences in susceptibility to toxicants between plan ktonic and littoral rotifers.