Devastating effects of exotic Nile perch invasion in L.Victoria

Saturday June 29 2024

Nile perch fish being delivered at weighing place in Jinja landing bay, Uganda on October 22, 2019. PHOTO | FILE | NMG


The introduction of the Nile perch into Lake Victoria has had devastating and long-lasting effects on the genetic diversity of its native cichlid species, according to a new study.

This artificial introduction has caused a significant ‘bottleneck effect,’ decimating many local fish population and altering the genomic structure of survivors, a group of scientists from Tanzania Fisheries Research Institute (Tafiri) and Tokyo Tech said.

In the 1950s, the Nile Perch was introduced into Lake Victoria to meet commercial demands for its meat.

However, by the 1990s, the predator had driven more than 200 species of endemic haplochromine cichlids to extinction. The impact on the genetic diversity of the surviving species has remained unclear.

Cichlids are an incredibly diverse family of fish that come in a rainbow of colors, and are predominantly found in Africa’s rift lakes. In just three lakes—Victoria, Malawi and Tanganyika—there are over 500 species.

Read: Pollution choking aquatic life, pushing fishers out of business


Researchers from Tafiri, Tokyo Institute of Technology, Sokendai, conducted large-scale comparative genomic analyses on multiple cichlid species endemic to Lake Victoria. Their findings, published in Molecular Biology and Evolution, reveal concrete evidence of the Nile perch’s impact.

The genomic analysis, which included 137 haplochromine species, showed that four species from the Mwanza Gulf, experienced a significant reduction in genetic diversity due to a ‘bottleneck event’.
“The timing of the bottleneck, which began during the 1970s–1980s and ended by the 1990s–2000s, corresponds to historical records of these endemic haplochromines’ disappearance and later resurgence,” explains Associate Professor Masato Nikaido from Tokyo Tech. This timing aligns with the introduction of the Nile perch for commercial purposes in the 1950s.
The study highlighted that the egg-eating cichlids Haplochromis sp. ‘matumbi hunter’ and Haplochromis microdon were particularly affected.
So severe was the bottleneck effect on the ‘matumbi hunter’ that its genome diverged significantly from closely related species. “This study presents, for the first time, the impacts of the Nile perch upsurge on the genetic structure of Lake Victoria haplochromines,” Peof Nikaido adds.

The loss of genetic diversity due to these bottleneck effects can hamper a species’ long-term fitness and adaptability. These insights underscore the severe consequences of introducing exotic species into ecosystems, even for species that survive extinction.

The research provides new insights into conservation biology, identifying species that need urgent protection and suggesting practical solutions like establishing no-fishing zones.

Some cichlid species previously thought extinct are gradually being rediscovered, offering hope for the resurgence of the ecosystem with well-informed conservation strategies.