Molecular Characterisation of Lernaea spp. (Anchor Worm) Infesting Cultured Fish in South East Nigeria

This study conducted a molecular characterisation of Lernaea spp. isolates collected from cultured fish exhibiting anchor worm infestations in Anambra, Imo, and Enugu states, South East Nigeria. Anchor worm infestations cause significant morbidity and production losses in Nigerian fish farms, yet the species-level diversity and molecular epidemiology of the parasite in the South East remain unresolved. Lernaea specimens were collected from 240 fish sampled across 15 farms, with specimens preserved in 70 percent ethanol and processed for DNA extraction. The mitochondrial cytochrome oxidase I (COI) gene was amplified using standard PCR protocols, sequenced, and subjected to phylogenetic analysis using maximum likelihood methods. Morphological characterisation was conducted in parallel. Results revealed three distinct molecular clusters, with Lernaea cyprinacea as the dominant species, accounting for 71 percent of isolates. A second genotypically distinct cluster shared 94 percent COI sequence similarity with Lernaea polymorpha, and a third cluster could not be resolved to known species, possibly representing an undescribed taxon or cryptic species. Geographic structuring was observed, with certain genotypes displaying regional clustering across the three states. Infestation intensity was significantly higher in earthen ponds than in concrete tanks, and in ponds with high organic loads. The study provides the first molecular characterisation data for Lernaea spp. in Nigerian aquaculture and recommends the integration of molecular diagnostic methods into routine fish health monitoring programmes to support targeted treatment and biosecurity management. Keywords: Lernaea, molecular characterisation, anchor worm, fish parasitology, South East Nigeria