Evidence of the Intrusion of the Oceanic Lightfish (Vinciguerria nimbaria) into Korean Waters Based on High-Throughput Sequencing of Mixed Fish Eggs

Abstract

The oceanic lightfish Vinciguerria nimbaria is a mesopelagic species found in tropical and subtropical waters. In this study, we collected a total of 266 mixed fish egg samples from 78 stations in Korean waters of the Northwest Pacific Ocean from January to November 2021, and analysed these samples for V. nimbaria using cytochrome c oxidase I (COI) metabarcoding. We detected V. nimbaria eggs five times in May and once in August, with 20 V. nimbaria eggs to be estimated among the 266 mixed samples, which consisted of 68,844 eggs. To verify the accuracy of the metabarcoding results, two samples consisting of 1 and 6 eggs (diameter, 0.82 ± 0.07 mm; n = 5), respectively, that were identified as V. nimbaria were reanalysed using partial COI regions with the Sanger sequencing method. COI sequences obtained using both sequencing methods showed 100% identity in the overlapping regions. The mixed eggs formed one clade with V. nimbaria (average pairwise genetic distance, 0.002 ± 0.003; n = 7) in a phylogenetic ML tree based on the mitogenome (2 rRNAs and 13 protein-coding genes) of order Stomiiformes, including partial COIs from the mixed egg samples. The pairwise genetic distances in this clade were smaller than that of Stomiiformes (0.468 ± 0.081), except for V. nimbaria. These eggs represent direct evidence of the intrusion or distribution of adult V. nimbaria, an unrecorded species, in Korean waters.