Recognition and Distribution of Two North Atlantic Gadiculus Species, G. argenteus and G. thori (Gadidae), Based on Otolith Morphology, Larval Pigmentation, Molecular Evidence, Morphometrics and Meristics

Abstract

The silvery pout genus Gadiculus consists of small aberrant codfishes with several extinct and currently only one recognized extant species. The oldest representatives of a Gadiculus lineage known from otoliths are Early Miocene in age. Fossil evidence has showed Gadiculus to originate from older genera diverging early from other true cods of the family Gadidae. As adult specimens of different species have been found to be highly similar and difficult to distinguish based on meristic and morphometric data, the number of species in this gadid genus has been controversial since different larval morphotypes were first discovered some 100 years ago. For almost 70 years, Gadiculus thori and Gadiculus argenteus have been considered subspecies only, with a distribution in the Northeast Atlantic Ocean including the Mediterranean. In this study, we resolve the long-standing issue of extant Gadiculus not being monotypic. New results in the form of distinct adult otoliths and molecular data unambiguously show two species of Gadiculus present—in agreement with larval morphotypes. Morphometric, meristic and molecular characters, as well as larval pigmentation are discussed in addition to present and past geographic distributions of the two taxa from distributions of fossil otoliths. At present, the cold-water species Gadiculus thori (northern silvery pout) is distributed in cold-temperate and subarctic latitudes in the Northeast Atlantic, including a new range extension off Southeast Greenland. Gadiculus argenteus (southern silvery pout) occurs in warmer waters and is distributed in the warm-temperate East Atlantic and Mediterranean. Fossil otoliths show that both species often co-existed in the Mediterranean from the Late Pliocene to the Middle Pleistocene.