# Insight Into Trophic Niche Differentiation in Labeobarbus (Cyprinidae) in the Luhoho Basin (Upper Congo Basin)

## TL;DR

This study explores how different mouth shapes in Labeobarbus fish in the Congo Basin relate to their diets and feeding habits.

## Contribution

The study provides new insights into trophic niche differentiation among Labeobarbus species based on mouth morphology in the Luhoho Basin.

## Key findings

- Chiselmouth species are more herbivorous/detritivorous, while rubberlip species are more insectivorous.
- Smiling phenotype fish show a distinct trophic niche, except in L. paucisquamatus where niches overlap.
- Isotopic niche modeling shows species-specific differentiation in feeding strategies.

## Abstract

Mouth morphology plays a crucial role in determining the trophic ecology of fish and sometimes underpins important lineage diversification. Freshwater teleost fish species belonging to the genus Labeobarbus, commonly found in Africa, exhibit intra‐ and interspecific variation and differences in the lower jaw occurring within and between species, respectively. Different phenotypes include a curved U‐shape (‘rubberlips’), a straight lower jaw (‘chiselmouth’) and an intermediate morphology known as the smiling phenotype. In some cases, smiling originates from hybridisation between chiselmouth and rubberlips. However, the trophic relationships of different mouth morphologies in the Labeobarbus taxa are still not well understood, particularly in the Congo Basin. Understanding the trophic ecology of Labeobarbus can enhance understanding of adaptive processes in morphologically diverse lineages. This study aims to investigate how differences in mouth morphology among multiple Labeobarbus species in the Luhoho River (Upper Congo Basin) link with different trophic niche uses. We combined information from gut morphometry, gut contents and stable isotope analyses on 202 fish specimens representing six species across four tributaries of the Middle Luhoho. All approaches consistently revealed trophic niche partitioning between chiselmouth and rubberlip species, respectively, more herbivorous/detritivorous and more insectivorous on the omnivory spectrum. In addition, trophic differences were also found between species within each mouth phenotype. Interestingly, the trophic niche of the smiling phenotype differed strongly from those of other phenotypes at all sites except for L. paucisquamatus, for which the trophic niches overlapped in Tchinganda. The pattern of trophic niche of Labeobarbus suggests subtle strategies to partition feeding resources when they occur across a narrow hydrographic scale.

Six Labeobarbus species occur in the Middle Luhoho, a left‐bank affluent of the Lowa River, including two chiselmouth species (Labeobarbus brauni, L. longidorsalis) and three rubberlip species (L. caudovittatus, L. longifilis, L. paucisquamatus), as well as an intermediate phenotype referred to as the smiling phenotype. Based on intestinal content and stable isotope approaches, chiselmouth species were found to feed on periphyton (algae, moss, and detritus), while rubberlip species were revealed to feed on insects. Isotopic niche modelling indicated that each species has achieved its isotopic niche differentiation. The intermediate phenotype tends to exhibit an intermediate value in its isotopic data. Nevertheless, the isotopic niches of L. paucisquamatus and intermediate (smiling) phenotypes overlapped, denoting that they could partially feed on the same food types.