The periodicity of primary increment formation in the otoliths of Arctic charr Salvelinus alpinus (L.)

Abstract

The role of environmental factors in the regulation of sub-annual increment formation in fish otoliths appears to differ markedly between species. To examine the periodicity of primary increment formation in the otoliths of 0 + Arctic charr, Salvelinus alpinus (L.), and the effects of temperature, and photoperiod on their formation, fish were held under controlled environmental conditions. Primary growth increments were found in the otoliths of fish held at constant temperature (18" C) and at ambient temperature [fluctuating with a circadian and circannual rhythm ( 4 1 8 " C)]. Consistent and significant disruptions in increment formation occurred however, in experimental groups subjected to rapid change from ambient photoperiod to a 6L : 6D photoperiod for 96 h. Disruptions in increment formation were also observed immediately following transportation of fish between holding facilities and following disease treatment. The number of otolith increments formed in fish held on an ambient photoperiod regime, correlated closely with time elapsed in days since checkmark formation (r =0.989, P<O.OOl) in fish sampled sequentially over a period of 10 to 105 days. Thus we demonstrate that under conditions of ambient photoperiod, primary increments are formed daily.

Environmental effects on primary increment formation in the otoliths of newlyhatched Arctic charr

“…The investigator must not be too hasty rejecting the use of increments to provide fish ages solely on the basis of a significance test without noting the magnitude of the deviation from daily. Adams et al (1992), while investigating increments in Arctic charr, found that increments were significantly not daily; however, the number of increments deposited after 100 days differed from 100 by only 3%.…”

“…Chinook salmon O. tshawytscha (Walbaum) did continue daily increment formation at 4 C (Neilson & Geen, 1982) with only reduced increment thickness. Adams et al (1992) have validated daily increments in Arctic charr held at ambient temperatures (4 to 18 C) with a 2 to 3 C daily fluctuation. In our study, otolith increment deposition was observed under all experimental conditions (1 to 7 C) and was daily among charr reared at 'higher' temperatures (5 to 7 C).…”

“…Validation methods have proven numerous times that when growth conditions are optimal, increments in otoliths of larval, juvenile and adult fish of many species, are formed on a daily basis (Marshall & Parker, 1982;Neilson & Geen, 1982;Ralston & Miyamoto, 1983;Volk et al, 1984;Rice et al, 1985;Jones & Brothers, 1987;Radtke et al, 1988;Dee & Radtke, 1989;Radtke et al, 1989;Radtke & Hourigan, 1990;Adams et al, 1992). It is important to realize which mechanisms affect the rate of increment formation in order to increase the accuracy and value of analyses which rely on this information.…”

Hatch timing of two subarctic salmonids in a stream network estimated by otolith increments

“…Growth increments are deposited daily at hatch and enumerating the increments has been used to estimate hatch dates reliably in many species including salmonids Stevenson & Campana, 1992;Tsukamoto et al, 1989;Yamamoto et al, 1997). Although cold temperatures typically reduce increment widths, increments have been successfully used to determine fish ages in salmonids subject to near-freezing temperatures (Adams et al, 1992;Nielsen & Green, 1982;. This method readily applies to young-of-the-year (YOY) individuals collected when field sampling has become feasible, and the individuals have become large enough for efficient capture during a snow-free period.…”

“…The field component of this study was preceded by a hatchery component using individuals with known hatch date ranges to validate age estimates and evaluate precision of age assignments among independent readers. Although otolith microstructural analysis has been applied successfully to infer hatch timing of both study species (Tsukamoto et al, 1989;Yamamoto et al, 1997), the age validation was deemed important because salmonids may deposit sub-daily increments on otoliths (Adams et al, 1992;Stevenson & Campana, 1992).…”