Geometric morphometric analysis of body shape and sexual dimorphism in Colossoma macropomum

Abstract

Background

This study investigates sexual dimorphism in Colossoma macropomum using geometric and linear morphometrics.

Methods

A total of 26 specimens (14 females, 12 males) were analysed through shape analysis (MorphoJ) and linear measurements (ImageJ). Statistical analysis of both linear and geometric morphometry was performed using the PAST program.

Results

Geometric morphometric analysis identified statistically significant differences in body shape between males and females. Females were characterised by a shorter and narrower body form, while males exhibited a longer and broader morphology. Notably, the caudal fin base's flexion axis, along with the position and length of the anal fin, were highlighted as key anatomical regions for distinguishing between adult males and females. Linear morphometric analysis further revealed significant sex-specific variations, particularly in the head region and anterior body width.

Conclusion

The findings integrate quantitative data from linear morphometric with visualised results from geometric morphometric analysis, providing a detailed assessment of morphological distinctions. Potential drivers of these differences, including reproductive strategies, feeding behaviours, population density, genetic structure, aquaculture practices, water depth, and ecological niche differentiation, were explored to explain the observed sexual dimorphism. This research provides valuable insights into the morphological variation and evolutionary mechanisms underlying sexual dimorphism in Colossoma macropomum, with implications for species management and conservation. Moreover, it represents a novel contribution as the first comprehensive study to utilise geometric morphometric techniques to elucidate shape differences between male and female individuals of this species.