This investigation was carried out using isolates of four algal species. Three cyanobacteria (Lyngbya perelegans, Oscillatoria accuminata and Phormidium valderianum) andone green alga (Spirogyra sp.) collected from Kafr Hakem (+ snails) and Sadek canals (- snails) in Giza Governorate, in addition to Nostoc muscorum obtained fromTheodor Bilharz Research Institute (TBRI).
Snails were fed separately on fresh algal species, on a combination of two species and on a mixture of the five algal species, during twenty weeks (5 months) and lettuce was used as control.
Growth rate of snails (shell diameter and height), infection rate and mortality percentage were recorded weekly during the experimental time.
Biomphalaria alexandrina and Bulinus truncatus snails fed on separate algal species, sublethal concentration of Phormidium valderianum (LC₀) and lettuce demonstrated the highest growth rates, while the lowest rate was recorded in Spirogyra sp. Using mixed food of two algal species, the maximum rate of snail growth was observed in snails fed on the LC₀ of Phormidium valderianum + Spirogyra sp, followed by those fed on Oscillatoria accuminata + Spirogyra sp. Snails fed on a mixture of all algal species exhibited the maximum growth rate.
The highest rate of infection and lowest percentage of mortality were recorded in both snail species fed on lettuce (59% & 19% for B. alexandrina and 77.3% & 10.7% for B. truncatus, respectively). The minimum rate of infection and maximum percentage of mortality were observed in snails fed on Spirogyra sp.
The nutritional value of the algal species and lettuce, using Carbon to Nitrogen ratio (C/N ratio), were analyzed and discussed on the light of the obtained results.