broken and narrowly spaced circuli followed by unbroken and more widely. For all succeeding years, spring and summer growth are characterized by widely spaced circuli (rapid length accretion) and fall and winter growth by closely spaced circuli (slow length accretion). We hypothesize that the pattern of circuli spacing and annulus formation are responses to photoperiod and food availability which the fish experience during their existence at sea. timing of annulus formation (2) to compare the rate of growth among Tenmile. The first annulus on many scales is barely discernable and is usually estimated by slight changes in the formation of the circuli (Figure 1). November indicating that one ring (annulus) was formed. Thus, annuli are formed about the time of the equinox and during a declining temperature regime. formed when a zone of closely spaced circuli is followed by a zone of widely spaced circuli. However, oceanic temperatures were declining at this time and do not reach minima until April. Annuli were formed between November and January. No significant variation in average spacing between circuli was explained by oceanic temperatures. and there was little circuli deposition between annuli Figure 2.3 (b). There were significant (p < 0.05) differences in the distance between circuli formed in the summer and in the two stocks for various years at sea. growth rates increase, producing wider circuli spacing and the formation of a. Radii cut the circuli present in their path. However, those fish forming their first annulus average 43. annual breeding cycle with a long interval in which the gonads returned almost to their virgin. Statistical analyses were conducted only on age 2.2 fish because of small sample sizes in four of the six years for age 2.3 fish. TABLE III: AVERAGE STANDARD LENGTHS OF FISH IN ANNULAR GROUPS Length Range, mm. At this time a pattern developed in which the circuli break off, branch, anastomose, and are generally irregular. Scales of the young fish showed no modification of the circuli until in the late spring. This pattern was persistent for fishes of two river systems, six year–classes and two age groups (2.2 and 2.3) and was due to summer growth. Length of fish from which scale was taken, 104 mm. The average distance between circuli formed during the second year of ocean growth is much less than that of first year or in subsequent years. This study describes a pattern of circulus spacing on the scales of sockeye salmon, Oncorhynchus nerka, which has not been reported previously. Circuli spacing and annulus formation: is there more than meets the eye? The case for sockeye salmon, Oncorhynchus nerka Circuli spacing and annulus formation: is there more than meets the eye? The case for sockeye.
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