Fish climbing in the upper Congo Basin (Central Africa), first report for the shellear Parakneria thysi on the Luvilombo Falls

Abstract

The ability of shellears to climb waterfalls has been known anecdotally for over 50 years. The behaviour is documented here for the first time, with supporting cinematographic and photographic evidence, for Parakneria thysi climbing the Luvilombo Falls on the Luvilombo River (lower Lufira). This is a size-related partial migration of thousands of small- to medium-sized individuals [~ 37-48 mm standard length (SL), while the maximum size is ~ 96 mm SL]. Specimens climb the vertical wall of the falls (~ 15 m high) in the splash zone during major floods, usually occurring at the end of the rainy season (April-May), using their pectoral fins, supported by their pelvic fins. Both pairs of fins have, on their ventral surface, pads bearing tiny unicellular hook-like projections. Additionally, their pectoral/pelvic girdle and fin rays also appear well-adapted for this capacity. They propel themselves vertically by lateral movements of the posterior part of the body as when swimming. Unfortunately, the Luvilombo River is exposed to serious anthropogenic impacts. The most important, albeit occasionally, is its complete desiccation during the dry season, resulting mostly from withdrawal of water for cropland irrigation, which undermines the ecological continuity of the river.