Abundance and annual distribution of freshwater snails and some trematode cercariae at Damietta Governorate, Egypt

In addition to being a good food source, freshwater snails are considered one of the positively
and negatively infl uencing invertebrates on the environment. Several biotic and abiotic factors are
thought to affect the distribution and the dynamics of these snails. Freshwater snails are the most
dominant and conspicuous individuals of the freshwater biota in Damietta Governorate. In this study,
freshwater snails were collected monthly from 5 geographically and environmentally different sites
at Damietta Governorate at the north of Egypt during June 2017-May 2018. Seven snail species;
Lanistes carinatus, Lanistes varicus, Pila wernei, Segmentorbis angustus, Melanoides tuberculata,
Biomphalaria alexandrina, and Gabbiella senoriansis, were identifi ed. Lanistes carinatus was the
most abundant species (56.4%) in the collection sites. Besides, Al-Inaniyyah village had the highest
snail species abundance and variety. The abundance of the most recorded species varied seasonally;
the highest abundance was recorded during summer while the lowest was during winter. The
abundance of some snail species correlated positively or negatively with some physico-chemical
parameters; water temperature, dissolved oxygen, conductivity, total dissolved salts, and electrical
conductivity. Two types of trematode cercariae; gymnocephalus cercariae and xiphidiocercariae,
were harvested from Lanistes carinatus. The highest prevalence of both cercarial types was detected
during summer. The correlation between the prevalence of both cercarial types and the physicochemical
parameters were determined. Xiphidiocercariae were the most predominant cercarial type
in Damietta Governorate. Our fi ndings suggest that the invasion of some freshwater snails is likely to
be the cause of the low prevalence or complete absence of some medically important intermediate
snail hosts. We recommend further characterization of the distribution of freshwater snails and the
interrelationships among them in Egypt, and suggest a controlled use of selected snail species to
combat their medically important analogues.
Keywords: Snails; cercariae; abundance; seasonal; physico-chemical; Lanistes