Distribution and Morphometric Variation Updates of Critically Endangered Peat Swamp Fish, Parosphromenus ornaticauda from West Kalimantan

Abstract

Parosphromenus ornaticauda is a critically endangered dwarf labyrinth fish restricted to peat swamp waters in West Kalimantan, Indonesia. Previous records were limited to the type locality, and morphological variation across its geographic range remained poorly understood. This study aims to update the distribution records and assess morphometric variation between sexes and populations. Field surveys were conducted at 20 locations across six rivers in West Kalimantan. Morphometric analysis was performed on 40 specimens (21 males and 19 females) from two populations using 13 body measurements. Statistical analyses included MANOVA, Mann-Whitney U test, and Principal Component Analysis. The species was recorded at seven locations, including five sites outside its IUCN distribution range, thereby extending its known occurrence to the Mempawah, Tempayan, and Ambawang rivers. Notably, only one location occurred within protected forest areas. Significant sexual dimorphism was detected in anal-fin base length, with males exhibiting shorter fins than females. Population-level differences were identified in five morphometric characters, with specimens from lentic peat-swamp habitats exhibiting smaller body depth and larger orbital diameter than those from lotic canal habitats. These results demonstrate that P. ornaticauda has a broader distribution than previously recognized and exhibits morphometric plasticity related to habitat type. Immediate conservation measures are recommended, given that the species occur predominantly in unprotected, fragmented habitats.