Evidence of intrusion of the oceanic lightfish, Vinciguerria nimbaria, into Korean waters based on high-throughput sequencing on the mixed fish eggs

Abstract

The oceanic lightfish, Vinciguerria nimbaria, inhabits the midwaters of tropical and subtropical waters of the world. We found eggs of this species in Korean waters located in the northwestern Pacific Ocean 4 times in May and once in August. The specimens were the 408 mixed fish eggs (71,104 eggs) collected in January-November 2021 and identified based on the COX1 barcode. The identification method was a COX1 metabarcoding useful for the mixed species. To verify the accuracy of the metabarcoding, two samples composed of a single egg and 6 eggs (diameter 0.83±0.03㎜) analyzed as only one species of V. nimbaria were re-analyzed by Sanger sequencing (SS) on the COX1 region. The two COX1 sequence reads analyzed by the two sequencing methods were 100% identical to each other. In the phylogenetic analysis, six clades were constructed by the maximum-likelihood tree analysis using the COX1 sequences from the genus Vinciguerria including those of fish eggs. The COX1 of the eggs was allocated in the same clade with the mitogenome reference of V. nimbaria. The mean genetic distance (0.0038±0.0069, n=231) of this clade was smaller than those of the mean genetic distance between the clades in the genus Vinciguerria (0.0731±0.0128; N=2742). These results would be proof of the intrusion of V. nimbaria unrecorded adults and imply that its northern spawning boundary is in Korean waters.