Recent reports suggested that when certain contaminants are present in aquatic ecosystem at levels higher the threshold, they would disrupt endocrine functions of a variety of aquatic invertebrates including rotifers. Prochloraz (C₁₅H₁₆C₁₃N₃O₂) was a new broad-spectrum fungicide developed by England Boots Company (now called Agro Evo) in 1974, and launched into the market in 1977. Previous studies have focused mainly on efficacy, toxicity, and fungicidal mechanism of prochloraz; however little information was available about its environmental hormone effect in aquatic ecosystem. This motivated us to use freshwater rotifer Brachionus calyciflorus, which was distributed widely in lakes, ponds, rivers and other such aquatic ecosystems, as test species to examine whether the fungicide prochloraz can affect the population growth and cumulative egg production in the rotifers and show environmental activity.
The effect of prochloraz on reproduction and life cycle characteristics in the rotifer B. calyciflorus was studied by using experimental methods under laboratory conditions. Neonate females of B. calyciflorus were (0-2 h old) hatched from resting eggs in EPA medium.This rotifer strain was originally collected in Huai-an, Jiangsu Province in China during 2002, and since then it has been cultured in the laboratory continuously with periodic collection and storage of resting eggs. Chlorella pyrenoidosa (cultured in HB₄ medium at 25℃) was fed to B. calyciflorus at a density 3.0×10⁶ cells /mL at 25℃.in 3 L bags under fluorescent illumination of 4000 lux and photo period was 16 ∶ 8(L ∶ D). The results showed that 24h median lethal concentration (24hLC50) value of prochloraz for B. calyciflorus was 7.09 mg/L, and exhibited a linear regression relationship Y=20.6581X-12.5673(R²=0.93), 95% limits are 6.95-7.21 mg/L. Survival curves were lower in treatment groups than that in control, and they decreased with increasing chemical concentrations. Prochloraz decreased the productivity of eggs significantly in treatments than in control (P<0.01). Population growth rate (r) and accumulative eggs production per female increased from 14 to 18 individuals with increasing concentrations of chemical from 0.04 to 0.18mg/L. Meanwhile, at higher concentrations of chemical (from 0.28 to 1.12mg/L),the population growth rate was inhibited. Cumulative eggs production declined with the increase of concentrations of chemical. The highest peak of net reproductive rate R₀ (18.33) appeared at a concentration of 0.71 mg/L, and the generation time (T) was prolonged with increase of chemical concentrations in treatments. The results suggested that prochloraz has lower toxic effect to B. calyciflorus and does not show obvious effects on reproductive rate and amictic female production. Though the rotifer B.calyciflorus showed lower sensitivity to prochloraz than fish Misgurnusmize lepis, it showed estrogen effect on rotifer B. calyciflorus.