Faecal DNA Metabarcoding for Diet Analysis of Endangered Fish Species, Odontobutis obscurus

Understanding the ecological characteristics of endangered species is essential for their management and conservation. The dark sleeper (<i>Odontobutis obscurus</i>) is a carnivorous freshwater fish that has been designated an endangered species in South Korea because of its highly restricted habitat range and small population size. However, ecological research on prey items for this species remains severely limited globally, posing challenges for establishing conservation measures such as translocation management. In this study, the food sources and feeding strategies of <i>O. obscurus</i> were identified through non-invasive faecal DNA metabarcoding. A total of 24 <i>O. obscurus</i> specimens were collected from Sanyang Stream on Geoje Island, and faecal DNA was amplified using mitochondrial cytochrome c oxidase I (COI) primer. As a result, 13 prey items were identified, comprising fish and benthic invertebrates. Dietary metrics revealed the overall food composition and major food source of <i>O. obscurus</i>, and the Costello method enabled graphical diet analysis, suggesting that <i>O. obscurus</i> is a generalist, feeding on a wide variety of food sources. The food selectivity index suggested that <i>O. obscurus</i> prefers specific prey items, such as genus <i>Misgurnus</i>, <i>Zacco</i> (fish), <i>Radix</i> (gastropod), and <i>Ephemera</i> (mayfly). This molecular method facilitated the diet analysis of an endangered fish species that cannot undergo dissection, providing crucial information for their management, particularly regarding translocation efforts.