Predator avoidance in Bulinus globosus (morelet, 1866) and B. tropicus (Krauss, 1848) (Gastropoda: Planorbidae) exposed to predatory and non-predatory fish

Abstract

The cichlid fish, Sargochromis codringtonii, has been suggested for biological control of freshwater snails, especially those serving as intermediate hosts for schistosomes. This study examined the behaviour of two aquatic snail species, Bulinus globosus and Bulinus tropicus, when exposed to water conditioned (defined as water inhabited by fish) by either Sargochromis codringtonii, a molluscivore, or Tilapia rendalli (Boulenger, 1896), a herbivore, and when exposed to predation risk in the presence of a refuge. Both snail species crawled above the waterline to a greater extent when exposed to water conditioned by S. codringtonii than when exposed to water conditioned by T. rendalli, or unconditioned water. Although the number of snails leaving the water tended to increase with the density of S. codringtonii, this was not statistically significant. While Bulinus globosus elicited a greater response to water conditioned by feeding fish than to that conditioned by non-feeding fish, B. tropicus did not respond differently to the two treatments. The introduction of S. codringtonii into tanks with a refuge caused snails to move actively into the covered areas.