Toothless predators: feeding performance and techniques among the piscivores within Lake Tana's endemic barbus species flock (Pisces:Cyprinidae)

Abstract

With more than 2000 fish species the Cyprinidae is the largest family of vertebrates. Lake Tana, a large lake (3050 km2) situated in the NW‐ highlands of Ethiopia, harbours, as far as we know the only remaining intact species flock of large (max. 100 cm FL) cyprinid fishes (15 Barbus spp.). One of the most intriguing aspects of this endemic Barbus species flock is the large number of piscivores (8). Cyprinid fishes seem not well designed for piscivory, they lack teeth in the oral jaw, have a small slit‐shaped pharyngeal cavity and all lack a stomach with low pH for digesting large prey. Many barbs are benthivorous species, like the ancestral barb in Lake Tana's isolated system. Why then is piscivory, which is rare among cyprinids, so common in Lake Tana Barbus? The aim of present study was to compare the performance and techniques of these piscivorous Barbus with known piscivores from other fish families. We studied prey handling times over prey size, prey capture using high‐speed movies, and assessed the effect of prey size on performance and prey selection in the field. Performances were explained by functional morphology of their feeding system. Overall, Lake Tana's piscivorous Barbus perform relatively ‘poor’, compared to piscivores from other fish families. For example, Lake Tana's piscivores are only able to handle prey fish smaller than 16% of their own body length. However, Lake Tana lacks potential piscivorous competitors, rendering the piscivorous Barbus by far the ‘best’ and apparently highly successful. They have adapted to all available macro‐habitats (littoral, offshore pelagic and offshore benthic), using different techniques (ambush, pursuit and cruising), a unique scenario for barbs.