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|Title: ||Laboratory breeding of biomphalaria pfeifferi and the isolation and charactisation of potential microbial pathogens for bioassay screening as molluscicides|
|Authors: ||Osei Kofi, Jonny|
|Issue Date: ||12-Dec-2001|
|Series/Report no.: ||2866;|
|Abstract: ||A biocontrol agent against the snail vectors of Schistosomiasis was searched for from freshwater bodies in some bilharzia endemic areas in the Ashanti region. Bioassays present inherent problems because of the inadequate supply of genetically comparable or identical snails from the field. Healthy field collected Biomphalaria pfeifferi snails were therefore bred under laboratory conditions to obtain snails from the same egg clutch that were of uniform genetic constitution, size, age and of sufficient quantities for bioassay experiments.
Biomphalaria pfejfferi was incubated in the laboratory in aerated sterile pond water until it spawned. The young snails were fed on centrifuged algal suspension and sun-dried lettuce until they began oviposition. This stock was multiplied in 9 litre plastic bowls and later transferred into large glass tanks where the multiplication process was allowed to continue to obtain several-folds of snails.
Monitoring of water quality involved measurement of pH, turbidity, dissolved oxygen, biochemical oxygen demand of the water. Water temperature was also measured. A temperature of 26°C ± 2°C and neutral pH range encouraged oviposition and growth. Dissolved oxygen (DO) of 7.2 mg l-1 and biochemical oxygen demand of 10 mg l-1 were also found to be favourable to the snails. The inclusion of Lemna, an aquatic plant helped to create a favourable water quality for snail breeding. Snail density of 3 or 4 per 250 ml of water gave better oviposition rates. A snail size range of 8 mm to 9 mm gave a better rate of oviposition.
Bacterial isolates were obtained from moribund Biomphalaria pfejfferi snails in the field and from soil sediments. Twelve isolates were obtained: eleven were found to belong to Bacillus cereus and one, Bacillus polymyxa.
Trials of bioassays were made using the laboratory bred snails. Each bioassay of a single isolate involved, at least, sixty snails of the same genotype between 6 mm and 10 mm size. Whilst the large scale laboratory breeding of Biomphalaria pfejfferi was highly successful, the pathogenicity of the isolates against the snails yielded negative results.
Bioassays were performed using bacterial isolates screened for from the field.|
|Description: ||A thesis submitted to the School of Graduate Studies,
Kwame Nkrumah University of Science and Technology in partial
fulfilment of the requirements for the award of Master of Philosophy degree, 2001|
|Appears in Collections:||College of Science|
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