FORMATION OF «FALSE ANNUAL RINGS» ON SCALE OF JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH IN LAKE KURSIN (LOWER KAMCHATKA RIVER)

During spring-summer flood (in June-July). transit underyearling of coho salmon, having or having no scales, migrate to Lake Kursin at the lower Kamchatka River, where resident coho salmon never spawn. In this case, additional zones of closely-spaced sclerites (ZCS) can be formed on their scale because of feeding change (additional ZCS of the 1st type). Seasonal growth restarts and annual zones of close sclerites (annual ring) form in middle May — early June on scales of yearlings and elder coho salmon wintered in Lake Kursin. These results contradict to the earlier conclusion of G.V. Bazarkin (2003) that the coho yearlings have no additional ZCSs in Lake Kursin, though the same collection of scale was analyzed. In late July — August, other additional ZCS can be formed on the scale of coho yearlings in the lake (additional ZCS of the 2nd type) that is next after the well-differentiated first annual ring. Possibly, the additional ZCSs were omitted by G.V. Bazarkin because of the scale measuring with high magnification — 113 times, without preliminary evaluation with lower magnification — 35–50 times, when the boundaries of certain or uncertain ZCSs are visible better. Rate of the sclerites forming was examined for coho juveniles of age 1+ by repeated observations in Lake Kursin in 2001 and evaluated as 15.60 days/sclerite between June 9 — July 1, 7.52 days/sclerite between July 1–21, and 7.94 days/sclerite between July 21 — August 30; on average one sclerite was formed in 10.35 days. The results demonstrate longer time of sclerites forming than reported earlier by G.V. Bazarkin (2003).

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