FORMING OF FALSE ANNUAL RINGS ON SCALES OF JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH IN THE UPPER REACHES, FLOODPLAIN OLD WATER BODIES AND LAKES IN THE MIDDLE AND LOWER REACHES OF THE KAMCHATKA RIVER

Structure of scales is investigated for coho salmon juveniles from several sites of their feeding in the Kamchatka River basin, from Pushchino (685 km from the river mouth) to Lake Nerpichye (at the mouth). The underyearlings begin their migrations over the river basin to individual plots soon after their emerging from nests, only part of them feed and winter at the spawning grounds (between Pushchino — Milkovo). A number of coho juveniles stay for feeding and wintering in the tributaries of the Kamchatka River, some of them migrate during spring–summer floods (mid May–June) to the old water bodies in its upper and middle reaches (near Milkovo, Dolinovka, Taezhny, Dedova Yurta, Lake Kulpik) and to the floodplain and lagoon–estuary lakes (Lake Kurazhechnoye, Lake Kursin, and others), having or yet having no scales. Aboriginal coho salmon never spawn in these floodplain water bodies, but the juveniles are observed there all the year round. After wintering, seasonal growth and forming a zone of closely-spaced sclerites of scale (ZCS) — annual ring start in early May or middle May (till early June for some individuals), both for coho yearlings and older juveniles. An additional ZCS (1st type) can be formed earlier on the coho scale in some lakes because of the feeding change. Besides, another additional ZSC (2nd type) can be formed on the scale of coho yearlings (1+) in the old water bodies at Dolinovka, Taezhny, Dedova Yurta, in the lakes Kulpik, Kurazhechnoye, Kursin, and Azabachye and in the Azabachya Channel (at the Dyakonovsky Brook) in late July — August because of seasonal changes in the feeding.

age, coho salmon yearling, scale, scleritis, annual ring, false annual ring

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