Impact of certain plants and synthetic molluscicides on some fresh water snails and fish

ABSTRACT

The LC50 [78, 85 ppm] and LC90 [88, 135 ppm] of Anagalis arvensis and calendula micrantha respectively against Biomphalaria alexandrina were higher than those of the non-target snails, Physa acuta, Planorbis planorbis, Helisorna duryi and Melanoides tuberculata. In contrast, the LC50 of Niclosamide [0.11 ppm] and Copper sulphate [CuSo4] [0.42 ppm] against B. alexandrma were lower than those of the non-target snails. The mortalities percentage among non-target snails ranged between 0.0 and 20% when sublethal concentrations of CuSo4 against B. alexandrina mixed with those of C. micrantha and between 0.0 and 40% when mixed with A. arvensis. Mortalities ranged between 0.0 and 50% when Niclosamide was mixed with each of A. arvensis and C. micrantha. A. arvensis induced 100% mortality on Oreochromis niloticus after 48 hrs exposure and after 24 hrs for Gambusia affinis. C. micrantha was non-toxic to the fish. The survival rate of O. niloticus and G. affinis after 48 hrs exposure to 0.11 ppm of Niclosamide were 83.3% and 100% respectively. These rates were 91.7% and 93.3% respectively when each of the two fish species was exposed to 0.42 ppm of CuSo4. Mixture of sub-lethal concentrations of A. arvensis against B. alexandrina and those of Niclosamide or CuSo4 at ratios 1040 and 2525 induced 66.6% mortalities on O. niloticus and 83.3% at 40 10. These mixtures caused 100% mortalities on G. affinis at all ratios. A. arvensis CuSo4 mixtures at 1040 induced 83.3% and 40% mortalities on O. niloticus and G. affinis respectively and 100% mortalities on both fish species at ratios 2525 and 4010. A mixture of sub-lethal concentrations of C. micrantha against B. alexandrina and of Niclosamide or CuSo4 caused mortalities of O. niloticus between 0.0 and 33.3% and between 5% and 35% of G. affinis. The residue of Cu in O. niloticus were 4.69, 19.06 and 25.37 mg/ l kgm fish after 24, 48 and 72 hrs exposure to LC0 of CuSO4 against B. alexandrina respectively