# High variability in chromosome number from a clade within the gourami family (Teleostei, Osphronemidae)

## TL;DR

This paper reports significant variation in chromosome numbers within a specific group of gourami fish, offering insights into evolutionary changes in their karyotype.

## Contribution

The study identifies a monophyletic clade with unusually low and variable diploid chromosome numbers in gouramis.

## Key findings

- Five species in the spiral egg clade have novel diploid chromosome numbers reported.
- High variability in chromosome arm numbers suggests large-scale mutations over time.
- The clade shows a reduction in diploid chromosome number during its evolutionary emergence.

## Abstract

Identifying clades with extensive and conspicuous changes in diploid chromosome number (2n) is an important step in unraveling the evolutionary mechanisms underlying karyotype evolution. Here, we report low 2n in a monophyletic group of teleost fishes within the family Osphronemidae defined by their unique spiral egg structure (the “spiral egg” clade). We sampled seven of the nine known species within the spiral egg clade, reporting novel 2n for five species and confirming two others. We find high variability in both 2n and chromosome arm number (fundamental number, FN), suggesting a 2n reduction during the emergence of the clade and numerous large-scale mutations across evolutionary time. These data provide important information in cataloguing 2n shifts in teleost fishes and highlight this group for further study in chromosomal and genomic evolution due to their karyotypic heterogeneity.