Animal behaviour: Tiny fish climb waterfalls (Scientific Reports)
3 April 2026
The first documented evidence of shellear fish (Parakneria thysi) climbing a waterfall in the Democratic Republic of the Congo is presented in Scientific Reports. The authors report that thousands of individuals — each measuring less than five centimetres — take around ten hours to scale the 15-metre-high waterfall by moving their fins and wiggling their bodies from side to side.
Vertical climbing has been observed in several distantly related fish species throughout the world, however, this behaviour is often poorly documented and reports in shellears have been anecdotal.
Pacifique Kiwele Mutambala, Emmanuel Vreven, and colleagues recorded thousands of shellears climbing the vertical walls of the Luvilombo Falls, Democratic Republic of the Congo, on four occasions in 2018 and 2020. They observed this behaviour carried out by fish measuring between 37 and 48 millimetres long towards the end of the rainy season (between April and May) in years of abundant rainfall. The authors observed shellears clinging to the vertical rock surface of the waterfall and propelling themselves upwards using their pectoral and pelvic fins (which have hook-like projections on their undersides), and sideways undulatory movements of the rear halves of their bodies.
The authors estimate that, on average, it can take an individual fish around nine hours and 45 minutes to climb to the top of the Luvilombo Falls. This includes 15 minutes of movement, 30 minutes of short pauses, and nine one-hour-long rests. They also note that fish are at risk of falling during climbing if they are hit by jets of water, particularly when climbing upside down to navigate around overhanging cliffs.
The authors propose that shellers may climb the Luvilombo Falls to reoccupy upstream habitats after being washed downstream in major rains, or to migrate to areas with lower food competition and fewer predatory fish, such as the silver butter catfish (Schilbe intermedius). They caution that fish waiting to climb the waterfall are at risk of being caught by fishers using illegal mosquito nets and that the biodiversity of the Luvilombo River may be threatened if the river is diverted upstream of the falls during the dry season to irrigate crops. They recommend comprehensive protection of the ecosystem.
- Article
- Open access
- Published: 02 April 2026
Kiwele Mutambala, P., Ngoy Kalumba, L., Cerwenka, A.F. et al. Fish climbing in the upper Congo Basin (Central Africa), first report for the shellear Parakneria thysi on the Luvilombo Falls. Sci Rep 16, 8509 (2026). https://doi.org/10.1038/s41598-026-42534-8
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