Scientists have discovered that barbs from Ethiopia's Lake Tana have remained virtually unchanged in their feeding habits despite catastrophic ecosystem changes. Even in the face of critical population declines, increasing pressure from invasive species, pollution, and turbid waters, different barbel species continue to feed differently: some feed on small fish, others on mollusks, and still others on insects and other resources. These observations will help better understand how to preserve the species diversity of lakes in densely populated areas of the planet. The results of the study, supported by a grant from the Russian Science Foundation (RSF), were published in the journal Ecology and Evolution.
During evolution, related groups of organisms descended from a common ancestor often quickly diverge into numerous new species. During this process, these emerging species acquire specific traits that enable them to adapt to different environmental conditions and new food sources. For example, in Lake Tana in Ethiopia, in just 16,000 years (a very short time by evolutionary standards), 15 species of African barbels of the genus Labeobarbus (fish of the Cyprinidae family) emerged.
Figure 2. Diversity of the Tang longhorn beetles of the genus Labeobarbus. Source: Evgeny Esin et al. / Ecology and Evolution, 2026.
Research in the 1990s revealed that barbel species varied greatly in appearance, habitat, and feeding habits (including predators, as well as species that feed on plankton, aquatic vegetation, mollusks, and aquatic insect larvae). However, until now, it was unknown how human activities over the past 30 years—lake pollution, dam construction, and overfishing—have impacted this diversity, ecological, and feeding preferences of African barbel.
Scientists from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS) (Moscow) and the Bahir Dar Fishery and Other Aquatic LIfe Research Center (Ethiopia) captured 11 African barbel species during an expedition to Lake Tana.
The authors collected muscle samples from all the fish and analyzed their stable nitrogen and carbon isotopes and fatty acids. Isotopes are varieties of the same chemical element that differ in mass.
Figure 3. Multidimensional scaling of the Tana barbels of the genus Labeobarbus based on fatty acid ratios. (a) — 95% confidence interval ellipses for each species are shown; (b) — factor vectors of fatty acids separating the species in the principal component space. Source: Evgeny Esin et al. / Ecology and Evolution, 2026.
"Depending on what fish eat, they accumulate different isotope ratios. The composition of fatty acids in their muscles also depends on diet. For example, high levels of short-chain omega-3 fatty acids are characteristic of fish that prefer zooplankton and aquatic insects, while an accumulation of omega-6 fatty acids indicates a diet of mollusks and algae," explains Boris Levin, a leading researcher at the A.N. Severtsov Institute of Ecology and Evolution at the Russian Academy of Sciences and the head of the project, which was supported by a grant from the Russian Science Foundation.
Using these markers, the authors determined that most of the captured barbel species continue to adhere to the same diet they had almost 30 years ago. Only a few species—likely due to human activity—have changed their dietary preferences. Predators have suffered the most in the ecosystem. For example, the barbel Labeobarbus platydorsus switched to a "mixed" diet due to reduced availability of prey, including mollusks and other benthic organisms in its diet, in addition to fish.
"We previously assumed that human activity would alter the dietary preferences of African barbels, disrupting the balance of matter and energy flows in the ecosystem. However, despite the critical decline in African barbel populations and changing habitat conditions, their dietary specializations have persisted. It's likely that the evolutionary mechanisms that led to the emergence of trophic niche diversity have proven to be relatively resilient to external changes. This discovery is important for preserving the species diversity of Lake Tana. Furthermore, it helps us better understand the processes of species formation in nature," explains Professor Evgeny Esin, Doctor of Biological Sciences, Head of the Laboratory of Lower Vertebrate Ecology at IEE RAS.