Abstract: We evaluated the toxicity of two commonly used aquaculture drugs, Galla chinensis extract and trichloroisocyanuric acid (TCCA), on the population dynamics of Euplotes sinica and Paramecium caudatum. Under hydrostatic conditions, acute toxicity test was conducted to investigate acute-lethal effects of both drugs, and subacute toxicity test was conducted to monitor the changes in population growth rate (r) and generation time (G) of two ciliates. The results showed that the LC₅₀ of G. chinensis extract to E. sinica and P. caudatum were 282.69 and 326.06 mg·L^-1, and 0.312 and 0.321 mg·L^-1 for TCCA, respectively. The sensitivity of both E. sinica and P. caudatum to TCCA was higher than to G. chinensis extract. The results of subacute toxicity test showed 112.58 mg·L^-1 G. chinensis extract and 0.24 mg·L^-1 TCCA had the strongest inhibition effects on population growth of E. sinica (P<0.01), with the growth rate being (0.43±0.036) d^-1, (0.39±0.004) d^-1, and generation time being (1.62±0.036) d, (1.77±0.002) d, respectively. The inhibitory effects of 135.3 mg·L^-1 G. chinensis extract and 0.25 mg·L^-1 TCCA on population growth of P. caudatum were the most significant (P<0.01), with the growth rate being (0.22±0.002) d^-1, (0.12±0.003) d^-1, generation time being (3.12±0.025) d, (5.84±0.175) d, respectively. High concentration of G. chinensis extract and TCCA could significantly inhibit population growth of the two ciliates. As an antibacterial drug, TCCA is safer than G. chinensis extract in aquaculture. Our results enriched the toxicological data of these two drugs on ciliates.

Key words: Euplotes sinica, Paramecum caudatum, trichloroisocyanuric acid (TCCA), Galla chinensis extract, growth rate, generation time