Fish age is determined by counting annuli, the zones of closely spaced circuli formed yearly during. The effects of sea lice alone cannot explain the observed shift in marine survival occurring in 2009. spaced saltwater growth circuli in scales of salmon. early attempts to validate age estimation from circuli of scales and annuli of. Therefore, the formation of fish annuli is seen as a result of not only seasonal water temperature changes but also changes in the process of fish growth (such as the role of genetics) through internal physiological mechanisms due to cyclical changes in the external environment, which is the result of physiological cyclical changes in fish. At this time a pattern developed in which the circuli break off, branch, anastomose, and are generally irregular. The relationship between circulus spacing and fish or scale growth rate is determined by the relative rates of growth and circulus formation. Scales of the young fish showed no modification of the circuli until in the late spring. Wild fish had faster PSG than untreated hatchery fish throughout the study period, but had slower PSG than treated hatchery fish during the early part of the time series. The periodicity of opaque annulus formation was determined by marginal. Length of fish from which scale was taken, 104 mm. During this later period, PSG correlated with the marine survival of salmon, whereas in the early period, this correlation was not evident. This transition was demarcated by the year 2009. Fish were sampled 13 times over a period of 25 months. If each annulus represented a year and the circuli appeared at regular intervals of time, then the number of circuli could vary but little.

Circuli at the annulus also sometimes cross over previously deposited circuli. However, the differentiation in PSG disappeared in the later portion of the time series, which coincided with a shift from low to higher marine survival. Scales were collected from Atlantic salmon raised in marine net pens off of the coast of Maine in order to characterize the formation of scale circuli and the growth of scales during the ocean phase, and to relate circulus deposition and scale growth rate to water temperature. formation of tightly spaced circuli in the formation of an annulus. PSG was greater in treated versus untreated fish in the early part of the time series, which was a period of low marine survival. Growth in the returning hatchery-reared fish was also compared to the growth of wild fish from the same smolt year class. The impact of sea lice on post-smolt growth (PSG) was studied by comparing growth patterns in the scales of recaptured adult salmon originating from hatchery-reared smolts that were untreated or were previously treated for sea lice infestation during the years 2003–2014.

Circuli spacing and annulus formation