The fish climbs cliffs for 10 hours to get over the waterfall

Scientists have just released rare documentary footage of a small fish called Parakneria Thysi (also known as shellear fish) measuring from 3.7 cm to 4.8 cm in the lower Congo River.

Theo Naturethis is one of the most extreme migrations in the natural world when fish have to directly confront gravity and fast water currents to conquer the top of a waterfall up to 15 m high.

Unlike most fish species that migrate by jumping over waterfalls, Parakneria thysi chooses the “climbing” method. Thousands of individuals gathered at the foot of the waterfall, taking advantage of the wet rock edges to inch their way higher. They begin their journey at the end of the rainy season, using small knobs on their pectoral and pelvic fins to cling to rocks, shake their hind bodies to create thrust and crawl up.

On average, each fish takes 9 hours and 45 minutes to complete the journey. However, this time is almost entirely devoted to rest, including nine hour-long breaks and 30-minute short pauses, for a total of only 15 minutes of movement. During that time, they face the risk of being swept away by currents or becoming prey for birds or fishing activities.

According to the magazine Scientific Reportsscientists recorded this activity four times in 2018 and 2020. The driving force behind this migration is the instinct to maintain the species. Above the steep waterfalls lies the peaceful upper reaches, with few predators and abundant food sources (such as algae and microorganisms on the rocks). Crossing the canyon helps Shellear fish occupy an exclusive habitat that is inaccessible to larger predatory fish.

The migration season is said to start in early April and end in May each year, when water levels drop at the end of the rainy season. Fish will climb the waterfall between 4:00 p.m. and 6:00 p.m., coinciding with sunset, while the lowest numbers are recorded at sunrise.

Despite possessing extraordinary adaptability, this fish still faces many risks from human fishing and irrigation.

The discovery of this fish’s activities not only enriches the treasure trove of the ecosystem of the Congo River – the deepest river in the world, but also helps environmental planners have a more cautious perspective when building hydroelectric projects, avoiding disrupting the special migration route of this fish.