Molecular Taxonomy of Deep-Sea Swallowers of the Family Chiasmodontidae ^†

Abstract

The taxonomy of deep-sea fishes remains a little explored and sometimes unclear subject, as is the case of the family Chiasmodontidae. In multiple fishery assessment surveys carried out between 2017 and 2021 in the Western North Atlantic, around 50 specimens of this family were caught and tentatively named onboard as Chiasmodon niger. To test this preliminary identification, based on taxonomic and geographical criteria, DNA barcodes of the 5′ end of the mitochondrial COI gene were developed for 37 specimens. In this way it was possible to observe the polymorphisms between sequences and to calculate the gene distance between each of them. GenBank and BOLD repositories were also used for presumptive identification based on the percentage of similarity between sequences. In addition, the sequences of the 37 specimens were compared with all the barcode records of the COI-5P region of chiasmodontids found in the BOLD database. From the comparison between all the sequences and the data analyses performed on them, two main conclusions were reached. The first is that all specimens captured in the Western North Atlantic area were confirmed to belong to the species Chiasmodon niger. The other conclusion that can be drawn is that the databases present major problems with regard to this family. The identification of the 37 sample specimens allowed the detection of misidentifications of some sequences extracted from the repositories, as well as possible synonymies, as is the case with Chiasmodon niger and Chiasmodon harteli. This highlights taxonomic conflicts that should be addressed as a subject for future studies.