Sex Differentiation of Hyporhamphus limbatus Based on Morphological Traits and Regression Relationships of Some Measurements

Hyporhamphus limbatus is a commercial value fish in the Mekong Delta, but little is known about its biological traits, especially sex differentiation using morphological characteristics and the regression relationship of some measurements, helping scientists avoid killing them in further studies; therefore, this study aimed to provide these data to this species. Samples were collected monthly at Phuoc Long and Dam Doi, using gillnets with a 1.0 cm mesh-size from May to July 2024. After collection, specimens were identified using morphological descriptions and preserved in 4 % formalin before transporting them to the laboratory for analysis. The morphological traits of 499 individuals were measured, including standard length (SL), body depth, head length, distance from the upper jaw to the dorsal fin, distance from the upper jaw to the anal fin, under jaw length, eye diameter, distance between eyes, mouth width, and tail height (CD). Males had a sharp-tipped upper jaw with asymmetrically dispersed black spots, while females had an arc-shaped, rounded upper jaw tip with evenly dispersed black spots. Males had a thin, orange-yellow upper jaw border and pale pink upper jaw surface, while females had a broader, greenish-yellow upper jaw border with a dark moss-green tip and 2 bright spots on their heads. The regression relationship between SL and CD could determine gender. Distinguishing fish sexes based on morphological traits helps reduce the number of specimens killed while studying the species’ population biology. The study highlighted the sex differentiation of Hyporhamphus limbatus through morphological traits and the regression relationship of some measurements. HIGHLIGHTS Description of differences in the upper jaw’s coloration and shape between males and females used for sex differentiation. A new method for sexing Hyporhamphus limbatus using morphology achieved 97.8 % accuracy. The regression relationship between Standard length (SL) and Tail height (CD) can help determine sex. Provide additional data on the species as a basis for future management and research of Hyporhamphus limbatus. GRAPHICAL ABSTRACT