LAUSR

The larvae and juveniles of Porocottus leptosomus belonging to the family Cottidae were collected (n = 95, 3.9–16.5 mm in body length, BL) from Busan, Korea, in March 2015. The larvae and juvenile were identified using DNA barcoding as P. leptosomus, and their morphological description was presented in detail. The yolk-sac larvae (3.9–5.6 mm BL) body was slightly compressed, the head was large, the eye was round and large, and the anus was before the middle of the body. The preflexion larvae (5.2–10.0 mm BL) body length drastically increased; caudal fin rays began to occur. The flexion larvae (9.4–11.8 mm BL) notochord flexion started; dorsal, pectoral, and anal fin rays began to occur; pelvic fin buds are seen; they possessed a pair of parietal spine; and a pair of supraocular cirri was first to develop. At 12 mm BL, the notochord was completely flexed. The larva stage (3.9–12.6 mm SL) had the stellate melanophores in the head, isthmus, gut, and tail (along to the ventral midline). During the juvenile stage (11.4–16.5 mm BL), melanophores covered the head and began to form five black bands on the side of the body. The larvae of P. leptosomus spent pelagic life, but moved to the bottom during the juvenile stage. The larvae and juveniles of P. leptosomus differ from other cottid larval fishes by body shape, melanophore head pattern, and spine development. P. leptosomus can be distinguished from Porocottus allisi by morphological development and the occurrence of larval fish: preopercular spine development, melanophore pattern, and caudal fin development.