Evaluating eDNA metabarcoding for fish biodiversity assessment in Nigerian aquatic ecosystems: potential, limitations, and comparisons with traditional methods

Fishery resources in Nigeria are experiencing a rapid decline, underscoring the urgent need for effective biodiversity surveys and comprehensive species documentation to guide conservation and management efforts. However, traditional methods for fish surveys, such as gillnets and trawl surveys, are intrusive, time-intensive, and costly. Environmental DNA (eDNA) metabarcoding has emerged as a non-invasive method for surveying fish diversity, yet its application in Nigerian aquatic ecosystems remains limited. This study evaluated the potential and limitations of 12S rRNA-based eDNA metabarcoding to survey fish communities across three water bodies (Jebba Hydroelectric Power Dam, Asa River, and Lagos lagoon). We also compared fish community composition obtained from our eDNA samples with previously published inventories based on traditional sampling techniques. Our study revealed several advantages of using eDNA metabarcoding for fish biodiversity surveys in Nigeria, including the rapid and non-invasive identification of fish taxa, the detection of differences in community composition and biodiversity metrics, the identification of species overlooked by traditional methods, and the ability to detect both threatened and invasive species. However, we identified three major constraints that must be addressed for the successful integration of eDNA sampling techniques in Nigeria. First are the logistical challenges, including determining the optimal number of replicates, selecting the appropriate water volume per site, determining the required number of sampling sites per study area, and identifying the most suitable time within the season for sampling. Second is the lack of a comprehensive DNA reference database for accurate species identification. Third are the issues with primer and marker specificity. Until a comprehensive regional DNA reference library is developed, suitable molecular markers are optimized, and standardized field protocols for eDNA sampling are established, we recommend using eDNA metabarcoding as a complementary survey tool rather than a replacement for conventional fish survey methods in Nigeria.