BIOLOGICAL STUDIES ON THE EFFECT OF SOME ALGAL EXTRACTS AGAINST BIOMPHALARIA ALEXANDRINA SNAILS

Abstract

Screening tests were carried out on 8 algal species belonging to 7 families to determine the molluscicidal ones. It was found that Dictyota dichotoma of Dictyotaceae family and Cystoseira barbata of family Sargassaceae were the most effective ones with LC50 values of 560 ppm and 2200 ppm, respectively against Biomphalaria alexandrina snails after 24 hours of exposure. Furthermore, the effect of prolonged exposure to sublethal concentrations LC5 (220 ppm), LC15 (660.7 ppm) and LC25 (1100 ppm) of aqueous extract of Cystoseira barbata and LC5 (56 ppm), LC15 (168 ppm) and LC25 (280 ppm) of Dictyota dichotoma algae was studied on survival rates of B. alexandrina snails, where snails treated with sublethal concentrations of D. dichotoma showed survival rates lower than those treated with sublethal concentrations of C. barbata. Prolonged exposure of snails to those sublethal concentrations also reduced the egg-laying capacity, and adversely affected hatchability of eggs. All the tested sublethal concentrations altered the structure of hermaphrodite gland, but the most pronounced effects were demonstrated by LC15 and LC25 of C. barbata and D. dichotoma algae, where some ova were degenerated and others were deformed, in addition, early stages of oogenesis and all spermatogenesis stages were highly affected. Moreover, these sublethal concentrations resulted in detrimental effects on the digestive gland of exposed snails. The most remarkable effects were vacuolation of digestive cells and degeneration of secretory ones. It was found that exposure of B. alexandrina to the sublethal concentrations LC5, LC15, LC25 for two weeks and LC5 for four weeks of both effective algae resulted in significant alteration (P < 0.05) in the activity of some enzymes, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) besides, total protein contents. The electrophoretic separation of haemolymph proteins from B. alexandrina snails showed different effects of the tested sublethal concentrations where some bands disappeared in the treated snails as compared with the control group.