Identification and Development of Larval and JuvenileUrophycis chuss,U. tenuisandPhycis chesteri(Pisces, Gadidae) from the Northwest Atlantic

Abstract

Pelagic stages of Urophycis chuss, Urophycis tenuis and Phycis chesteri from the Northwest Atlantic were identified by differences in caudal fin-ray and epibranchial gillraker counts, body depth and pigmentation. The adult complement of caudal fin rays in U. chuss (28-34, mean 31.5) and U. tenuis (33-39, mean 36.5) distinguished larvae greater than 7-8 mm SL (standard length). Caudal fin-ray counts in P. chesteri (32-35, mean 33.3) overlapped those of the two Urophycis species. The adult complement of epibranchial gillrakers in U. chuss (3), U. tenuis (2) and P. chesteri (4-5) developed at 12-14 mm in Urophycis and at 16-·18 mm in P. chesteri. Phycis chesteri was deeper-bodied (24.4% SL) than U. tenuis (21.3% SL) which in turn was deeper-bodied than U. chuss (19.3% SL). Pelagic larvae and juveniles of the three species had 3 pelvic fin rays. A size-dependent key to pelagic stages of these species is presented. Black pigment on pelvic fins of pelagic Urophycis and Phycis was absent in newly-demersal specimens. Differences in pigmentation on the midline, pectoral fin base, dorsa-lateral trunk and caudal peduncle helped to separate 5-10 mm Urophycis larvae. Ossification generally occurred at a smaller size in U. ctiuss than in either U. tenuis or P. chesteri for most ofthe structures examined. The mandibular arch, dentary, premaxilla, precaudal vertebrae, branchiostegals, cleithra and parasphenoid ossified first. Pelvic fins were the first fins to develop. The first dorsal fin and the pectoral fins developed last.