Abstrak
Mentarang Hulu River in Malinau Regency is a natural habitat with various vegetation along the river banks and it still has minimum human activity. This river has a width of 60-70 meters, fast-flowing water, and many riffles, which are natural conditions of the river as well as its unique characteristics that support the life of various fish species. However, information regarding the presence of fish in Mentarang Hulu River is still very limited and has not been extensively studied scientifically. This research aimed to identify fish in Mentarang Hulu River and the relative abundance of each species in order to determine the composition and dominance of existing types. Samples were collected from the catch of fishermen using two fishing gear types: nets and gillnets. Fish identification was performed by referring to identification books. Fish identification is carried out by observing morphological shapes such as the shape of the mouth, head, fins, tail, as well as the color and pattern of the body. The study was conducted over 2 months from January to February 2025. A total of 570 samples were collected, distributed into 1 phylum, 1 class, 3 orders, 4 families, and 13 genera. The analysis results showed that the Niem fish species (Osteochilus spp.) has the highest abundance at 31.75%, followed by Lalang fish (Parachela spp.) at 20.18%, and Pelian fish (Neolissochilus spp.) at 16.67%. The lowest abundances were found in Benteur fish (Barbodes spp.) at 0.18%, Garra fish (Garra borneensis) at 0.53%, and Tilan fish (Mastacembelus spp.) at 0.53%.