The growth rate was related more closely to day length than to other variables examined. Circuli spacing and annulus formation: is there more than meets the eye The case for sockeye salmon,Oncorhynchus nerka. 0.2 C) did not arrest metabolic activity. Circuli spacing and annulus formation: is there more than meets the eye The case for sockeye salmon, Oncorhynchus nerka Barber, W. These results corroborate previous research on scale characteristics and growth, while providing novel evidence that highlights the importance of water temperature in these relationships. The temperature of the water during the winter (50 ±. In a multiple linear regression, median circulus spacing and water temperature accounted for 68 of the variation in observed O. The distance from the focus to the first annulus decreases on some scales the first annulus marks a sharp discontinuity between a 0+ zone of closely spaced circuli and a subsequent zone of widely spaced circuli (Figure 6). Fish were always given all the food they would eat to eliminate availability of food as a factor of mark formation. Most fish grew throughout the winter the only exceptions were one bloater ( Coregonus hoyi) and several of the largest lake whitefish ( C. The accessory check formed during a period of declining temperatures (1-5 degrees F, or 0.6-2.8 degrees C, per month) and of little change in growth or declining growth. The annulus formed during a period of constant temperatures and of little change in growth or increasing growth. Both marks had all the usual characteristics of an annulus but the spring mark was considered the annulus and the fall mark an accessory check. The stronger formed during March-April and the weaker in October-November. Two marks formed on almost all scales each calendar year. January 1 and the time of annulus formation in spring or early summer are. Scales were also examined from fish that died and from preserved specimens of young-of-the-year for each species. feeding and growth resume, new circuli form that are spaced further apart. Scales were taken monthly from marked fish for periods up to 21 months. Whetherscale circulus spacing can be used to estimate fish growth ratedepends on whether scale growth and circulus deposition rate are re lated to fish growth rate in a con sistent, predictable manner. Scales from known-age coregonids reared in the laboratory were examined to determine when annuli formed and to learn possible factors of their formation. Spacing ofscale circuli is determined byboth the rateat which circuli are formed and therateofgrowthofthe scale.
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