# Eye-sidedness does not drive differences in growth and maturation in the Indian halibut (Psettodes erumei) from the Western Arabian Gulf

## TL;DR

This study finds that eye-sidedness in Indian halibut does not affect growth or reproduction, suggesting it evolved due to developmental factors rather than adaptive advantages.

## Contribution

Demonstrates that eye-sidedness in P. erumei is not linked to growth or reproductive advantages, challenging assumptions about adaptive asymmetry in flatfishes.

## Key findings

- Sex, not eye-sidedness, primarily influences growth and length–weight relationships in P. erumei.
- Eye-sidedness has no significant effect on reproductive traits like gonadosomatic index or maturity length.
- Minor body shape differences exist between morphs but are likely biologically negligible.

## Abstract

The Indian halibut Psettodes erumei (Family Psettodidae), a primitive lineage of flatfishes exhibiting both sinistral and dextral morphs, provides a unique model for examining the evolutionary significance of morphological asymmetry in flatfishes. This study tested whether eye-sidedness influences somatic growth, body shape, and reproductive traits in P. erumei from the western Arabian Gulf. A total of 215 individuals were collected between 2020 and 2022, with sinistral and dextral morphs occurring in near-equal proportions. Model selection based on Akaike weights revealed that sex, rather than eye-sidedness, was the primary factor influencing length–weight relationships and growth, with females attaining significantly larger asymptotic lengths. Eye-sidedness had no detectable effect on gonadosomatic index patterns or length at 50% maturity. While Procrustes regression detected statistically significant differences in body landmarks and semilandmarks between morphs, these differences were minor and likely biologically negligible. Overall, the results support the hypothesis that eye-sidedness in P. erumei does not confer a measurable evolutionary advantage and imply that differences in developmental mechanisms, rather than adaptive advantages, played a primary role in fixing directional asymmetry in most flatfish lineages. Future research into the molecular and developmental pathways governing eye-sidedness will be essential for understanding why the vast majority of flatfish species exhibit monomorphic asymmetry.

The online version contains supplementary material available at 10.1038/s41598-025-30930-5.