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

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, Helisoma duryi and Melanoides tuberculata. In contrast, the LC50 of Niclosamide (0.11 ppm) and Copper sulphate (CuSO4) (0.42 ppm) against B. alexandrina were lower than those of the non-target snails. The mortalities percentage among non-target snails ranged between 0.0 & 20% when sublethal concentrations of CuSO4 against B. alexandrina mixed with those of C. micrantha and between 0.0 & 40% when mixed with A. arvensis. Mortalities ranged between 0.0 & 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% & 100% respectively. These rates were 91.7% & 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 10:40 & 25:25 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 10:40 induced 83.3% & 40% mortalities on O. niloticus and G. affinis respectively and 100% mortalities on both fish species at ratios 25:25 & 40:10. 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 & 33.3% and between 5% & 35% of G. affinis. The residue of Cu in O. niloticus were 4.69, 19.06 & 25.37 mg/1kgm fish after 24, 48 & 72 hrs exposure to LC0 of CuSO4 against B. alexandrina respectively.

Feeding ecology and food composition of the black carp Mylopharyngodon piceus and the grass carp Ctenopharyngodon idella inhabiting the fish pond of Al-Abbassa fish hatchery with emphasis given to vector snails

Stomach contents of M. piceus and C. idella collected from earthen fish ponds at Al-Abbassa fish hatchery during different seasons were examined. Food items were analyzed by three methods; the numerical (N%) percentage of point assessment (P%) and frequency of occurrence (F%). A comparison of the different methods emphasized the importance of snails as the major food resources in the diet of M. piceus during all seasons. During winter, stomachs of the most fish samples collected from fish ponds were empty or had traces of food. The index of relative importance (I.R.I) indicated that snails were the major food category in the diet of M. piceus during summer, autumn and spring represented by 7331, 9696 and 11670 respectively. Plants were the main food item in the diet of C. idella during summer (4604), meanwhile they came 3rd in relative importance in the diet during autumn and spring. Artificial fish food came as the 2nd food item in the diet of M. piceus during summer (1398.9) and autumn (5896.3) but it completely absent in spring. It is considered the main food item in diet of C. idella during autumn (10384.3) and spring (6293.5) and being 3rd in summer (1395.5). The results showed that snails reached highest level in the diet of M. piceus during spring (about 80% of all diet, decreased during summer (about 70%) and reached lowest proportion in autumn (50%). Plants exhibited marked seasonal variation in abundance with maximum level during summer (about 41% of all diet decreased during spring (27%) and autumn (22%). Artificial fish food was the highest in the diet of M. piceus during autumn (39%), decreased in summer (22%) until disappeared during spring. It reached highest level in diet of C. idella during autumn (49%), decreased in spring (38%) and reached lowest proportion during summer (21 %).

Susceptibility of Biomphalaria alexandrina to the plant Azolla pinnata and some herbicides in relation to infection with Schistosoma mansoni miracidia

Molluscicidal activity of the herebicides 2,4-D and Graminol, as well as both extracts and dry powder of the plant Azolla pinnata were evaluated against B. alexandrina snails. It was observed that 2,4-D proved to be the most toxic compound among he tested ones, showing LC90 of 52 ppm after 24 h of exposure. Ethanol extract of Azolla showed the highest molluscicidal activity against the tested snails compared with the other extracts and dry powder (LC90 = 3300 ppm). Ethanol extract at 6600 ppm after 3 h of exposure killed 100% and 19.4% of S. mansoni miracidia and cercariae, respectively. The molluscicidal activity of 2,4-D was not influenced by the presence of Azolla (900 plants/liter) for 7 days, while Graminol effect was significantly reduced. However, the infectivity of S. mansoni miracidia to B. alexandrina snails was not affected by Azolla existence.

Effect of the plant Azolla pinnata on survival, growth rate, fecundity and hatchability of egg-masses of Biomphalaria alexandrina snails

Data indicated that Azolla pinnata plants variously reduce the growth rate of Biomphalaria alexandrina snails expressed as net increase in shell diameter (direct or indirect exposure). The plant density played an important role in this respect. The higher the plant density was the lower the growth rate and vice versa. Too, indirect exposure of newly hatched B. alexandrina resulted from exposed treated eggs reduced the growth rate of these snails. Data revealed that direct and/or indirect exposure to the abnormal high density (50,000 plants/L) resulted in complete kill of B. alexandrina snails after two weeks from continuous exposure. Snails exposed directly to Azolla at 50,000 and 25,000 plants/L failed to lay eggs. On the other hand, sanils exposed to 10,000 plants/L laid few eggs, resulted in low reproductive rate (57.94) compared with unexposed ones (110.6). The same trend of results was recorded with hatchability of Biomphalaria eggs.