Аннотация:Experimentally studied the effect of pH fluctuations in water on theduration of life, swimming speed, photoreactions and georeactions cercaria Cryptocotylelingua, C. concavum Himasthla elongata, Cercaria parvicaudata. It was found that inthe range of fluctuations in the pH of seawater from 8.25 to 6.25 with decreasing pH,life expectancy also decreases. A decrease in pH from 8.5 to 6.0 leads to a slight de-crease in swimming speed and positive georeaction of the larvae. Changes in the pHvalues of sea water do not affect the manifestations of the photoreaction of the studiedcercariae.