The effects of salinity, pH and temperature on the half-life and longevityof Echinostoma caproni miracidia

Miracidia of Echinostoma caproni were exposed to solutions varying in salin ity, pH, and temperature in 1 ml concavity slides. Half-lives of the miraci dial populations were determined and longevity curves constructed to find m aximum life spans of the miracidia in the different conditions. Control mir acidia in aquarium water at pH 7.2 and 22 degrees C. had a half-life of 3.6 h and a maximum life span of 9 h. Miracidia of E. caproni were not very to lerant of saline solutions from 0.1% to 0.4%, the latter being lethal withi n an hour. A bimodal effect was found with exposure to aquarium water of va rying pH, with a peak at pH 5 in acid solutions and pH 9 in alkaline soluti ons. Miracidia tolerated pH ranges from 3 to 11 exhibiting half-lives of 2. 4 h or greater in these solutions. At lower than ambient temperatures, E. c aproni miracidia lived longer, the greatest being a half-life of 5.0 h and a maximum life span of 15 h at 5 degrees C. At warmer temperatures, the hal f-life was reduced until lethality was reached at 40 degrees C. ANCOVA anal ysis of log transformed longevity curves supported the observation that in pH trials many miracidia survived initially with a major die-off after 3.3 h. The opposite trend of early die-off and gradual mortality of the survivo rs was supported in the temperature trials.