Primary Dispersion and Some Morphological Characteristics of Migrating Larvae of the Sakhalin Sculpin Cottus amblystomopsis (Cottidae) in the Malaya Khuzi River (Sakhalin)

Migration of Sakhalin sculpin Cottus amblystomopsis larvae from the river to the sea for early rearing—the primary dispersion, occurs in the form of passive downstream migration in the first 1.0–1.5 h after dark. Reaction of larvae to decrease of illumination ensures their involvement into the flow and the implementation of downstream migration. Total duration of primary dispersion period does not exceed 3 days. Body length of the larvae is on average 7.7 mm, their vertebrae and spinous processes are formed, the anlages of unpaired fins are noticeable, and pectoral fins are well developed.