Distinguishing small juvenile Atlantic cod ( Gadus morhua) from Greenland cod ( Gadusogac) by comparing meristic characters and discriminant function analyses of morphometric data

Abstract

Two biochemical, 7 meristic, and 14 morphometric characters in addition to total body mass were examined to determine which characters best distinguish demersal Gadus ogac from Gadus morhua over the size range 87-135 mm standard length. These congeneric species of cod (Gadidae) remain difficult to distinguish where they co-occur in coastal habitats as recently settled juveniles. Consequently, surveys that target young demersal cod (G. morhua) in coastal nursery areas may be biased, owing to misidentifications. The electrophoretic mobilities of esterase and creatine kinase proteins unambiguously distinguished G. ogac from G. morhua. Of the 14 morphometric characters examined by means of discriminant function analyses, eye diameter and body depth at the origin of the second dorsal fin in addition to total body mass best separate G. ogac from G. morhua over the size range examined. In general, G. ogac has smaller eyes and is heavier and deeper bodied than G. morhua. Counts of vertebrae and of dorsal, anal, and caudal fin rays overlap between species. The shape of the lateral line and especially body coloration are additional characters that help to distinguish these species in the field. Gadus ogac are usually bottle green when freshly caught, whereas G. morhua are usually brownish in dorsal and lateral coloration. Gadus ogac also often have a more strongly arched lateral line than G. morhua of a similar size. All juvenile cod collected along the northeast coast of Newfoundland in this study were either G. ogac or G. morhua. Microgadus tomcod, another gadid common in coastal habitats, was not collected.