Simulated field trials to evaluate the effect of Sargochromis codringtoni and Tilapia rendalli on snails in the presence and absence of aquatic plants.

Abstract

Two cichlid fish were studied under semi-natural conditions to evaluate their potential as agents for the biological control of schistosome intermediate host snails. 42 enclosures (60 × 60 × 100 cm) were placed along 2 edges of a pond and all plants were removed. In half of the enclosures, 2 plants each of Ludwigia stolonifera, Nymphaea caerulea and Lagarosiphon major were planted. Four weeks after the enclosures were erected and when the plants had established, 228 wild-caught Bulinus globosus, 61 laboratory-bred Biomphalaria pfeifferi and 191 laboratory-bred Bulinus tropicus were introduced into each enclosure. On week 11 after introduction of the snails, a single Sargochromis codringtoni (which is known to eat snails) or a single Tilapia rendalli (which survives primarily on aquatic plants but may ingest snail egg masses and juvenile snails) was introduced into each of 7 enclosures with plants and 7 enclosures without plants. S. codringtoni reduced snail numbers significantly, but this effect was less pronounced when plants were present. T. rendalli did not significantly reduce the biomass of aquatic plant species used in the experiment, but did significantly reduce snail numbers, albeit to a much lesser extent than observed for S. codringtoni. It is concluded that the 2 fish species may complement each other in the control of schistosome intermediate host snails, but further investigations are needed to determine whether they can co-exist in nature, and the extent to which T. rendalli can control other species of aquatic plants under natural conditions.

Key words

• aquatic animals
• aquatic invertebrates
• aquatic organisms
• aquatic plants
• biological control
• biological control agents
• control
• freshwater fishes
• freshwater invertebrates
• freshwater molluscs
• helminthoses
• helminths
• hosts
• human diseases
• infections
• intermediate hosts
• natural enemies
• parasites
• parasitoses
• schistosomiasis
• snail-borne diseases
• trematode infections
• trials