The first records of walleye pollock Gadus chalcogrammus Pallas, 1814 in the seas of the Siberian Arctic (the Laptev Sea, the Kara Sea, the southeastern Barents Sea), are documented. Information about the external morphology (morphometric and meristic characters), photos of sagittal otoliths and fish, and data on the sequences of the CO1 mtDNA gene are presented. The results of a comparative analysis indicate that walleye pollock caught in the Siberian Arctic do not differ in principle from North Pacific and North Atlantic individuals. Previous conclusions about the conspecificity of the walleye and Norwegian pollock Theragra finnmarchica are confirmed. New captures of walleye pollock in the Siberian Arctic allow us to formulate a hypothesis about its continuous species’ range from the coasts of Norway in the North Atlantic to the coasts of Korea, Japan, and California in the North Pacific. The few records of walleye pollock in the North Atlantic originate from the North Pacific due to the transport of early pelagic juveniles to the Arctic by currents through the Bering Strait and further active westward migrations of individuals which have switched to the bentho-pelagic mode of life.

A single specimen of the northern wolffish Anarhichas denticulatus Krøyer, 1845, 393 mm in length, was documented for the first time in the Siberian Arctic (Laptev Sea, Russia). Species identification was confirmed by an integrative taxonomic approach that included examination of external morphology and DNA barcoding using the COI mtDNA gene. This species is widely distributed in the North Atlantic, but records in the Arctic Ocean are limited to the Canadian and US coasts. This record might represent a significant range extension of about 7500 km for the species and may be associated with the eastward transport of a pelagic juvenile specimen from the Northeastern Atlantic to the Laptev Sea by the North Atlantic current, consistent with the hypothesis of Atlantification of the Arctic Ocean. X-ray images of the Laptev Sea specimen and photographs showing ontogenetic variations of species’ coloration are provided for reference. The Laptev Sea specimen had a more elongated shape, longer preorbital distance, and longer pectoral, dorsal, and anal fins, as well as a larger eye and wider caudal fin compared to North Atlantic samples. The size differences are likely associated with conditions experienced as a juvenile during the pelagic stage of the lifecycle.