Morphological characteristics, sexual dimorphism, and growth of coolie loach (Pangio kuhlii Valenciennes, 1846) from Tay Ninh province, Vietnam

Abstract

Coolie loach (Pangio kuhlii) is a freshwater fish species native to Vietnam, holding significant economic value in the ornamental fish export market. This study was conducted from September to December, 2025 to supplement the biological database of this species, serving as a premise for artificial reproduction research, thereby contributing to conservation and sustainable development of aquatic natural resources. Morphological analysis of 80 specimens collected from Tay Ninh Province were relatively small, with standard length ranging from 4.11 to 7.07 cm. The body is elongated and laterally compressed, with 7 to 12 brown stripes on each side. The head is wedge-shaped, tapering anteriorly, and proportionally small relative to total body length. The mouth is subterminal, horseshoe-shaped, bordered by three pairs of well-developed barbels. Sexual dimorphism was evident in the external morphology of the pectoral fins. Males are distinguished by the presence of a stiffened first pectoral-fin ray and the body is slender and elongated, whereas females lack the stiffened ray and the abdomen is larger and more rounded. The Relative Gut Length (RLG) index of 30 specimens was less than 1 (ranged from 0.7630 to 0.7743); indicating that the species is carnivorous. Moreover, analysis of 50 specimens showed a strong length - weight relationship was expressed by the equation W=0,0028*L^3,21, demonstrating a strong positive allometric growth pattern R²=0.8863.