Prey selection under laboratory conditions by pond-bred Trematocranus placodon (Regan, 1922), a molluscivorous cichlid from Lake Malaw̌i

Abstract

Trematocranus placodon, a predator of freshwater snails in Lake Malaw̌i, has been recommended for the control of schistosome intermediate hosts in aquaculture ponds. Fish from Lake Malaw̌i were introduced into a pond close to Lilongwe and we attempted to elucidate whether pond-raised F 1 retain their ability to consume snails. In laboratory experiments, small fish (70-80mm total length) preyed only on Bulinus tropicus while fish of the 100-110mm and the 120-130mm size classes also chose B. globosus. All three size classes of fish preferred B. tropicus, which was abundant in the pond where fish were raised. Bulinus nyassanus was consumed by the largest fish only. Melanoides tuberculata was not preyed upon, although this species dominates stomach contents of field collected T. placodon. T. placodon is a pharyngeal crusher and comparisons of the size and dentition of the pharyngeal bones revealed some differences between field collected and pond-bred fishes. Although pond-bred fishes are able to crush snails, the development of the pharyngeal teeth should be better controlled by fish diet. A hard diet early in life is a prerequisite for T. placodon to develop molariform teeth. Later once molariform teeth are developed, fish can be transferred to pond conditions for grow-up and snail control. © 2012 Taylor & Francis.