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<br />\~q~ ~t~~~~~() <br /> <br />Transactions of the American Fisheries Society 127:105-117, 1998 <br />@ Copyright by the American Fisheries Society 1998 <br /> <br />1{Dd.\ <br /> <br />Environmental Factors Affect Daily Increment Deposition and <br />Otolith Growth in Young Colorado Squawfish <br /> <br />. <br /> <br />KEVIN R. BESTGEN1 AND JAY M. BUNDY <br /> <br />Larval Fish Laboratory, Department of Fishery and Wildlife Biology <br />Colorado State University, Fort Collins, Colorado 80523, USA <br /> <br />Abstract.-Otolith microstructure of endangered Colorado squawfish Ptychocheilus lucius was <br />investigated to determine patterns of otolith growth and to validate daily deposition of increments. <br />Sagittae and lapilli formed prior to hatching. After fish hatched, otolith increments were deposited <br />daily whether larvae were reared at a constant 220C temperature or subjected to fluctuating tem- <br />peratures (:t2.50/d) centered at 18, 22, or 26"C. Otolith increments were clearer and counts of <br />increments were more accurate for fish reared at fluctuating than at constant temperatures. Otolith <br />growth was lower at 180C than at 22 or 260C, but evidence of a direct effect of temperature on <br />otolith growth was inconclusive, Lapillus diameters of slow-growing Colorado squawfish were <br />larger than those of similar-sized but fast-growing fish, indicating that fish and otolith growth rates <br />were not proportional. When larvae were starved, growth in body length generally ceased im- <br />mediately but otolith growth continued for up to 15 d, Otolith growth was reduced for up to 5 d <br />after starved fish began to feed. Timing of starvation and reduced growth may not be accurately <br />recorded by reduced otolith increment spacing. Low-contrast otolith increments in wild fish may <br />illdicate periods of low food abundance and starvation, Increased otolith growth early in life could <br />reflect the start of exogenous feeding by Colorado squawfish larvae, a habitat ~hift to warmer <br />water, or both, Otolith analysis will be useful for elucidating age, growth, and recruitment patterns <br />of young Colorado squawfish, <br /> <br />t, <br /> <br />Numbers of daily increments in fish otoliths, <br />patterns of increment deposition, and otolith <br />growth rates may record life history events such <br />as hatching, growth stanzas, periods of physiolog- <br />ical stress, movements, and changes in water tem- <br />perature or food abundance (Methot 1983; Cam- <br />pana and Neilson 1985; Penney and Evans 1985; <br />Rice et aI. 1985; Eckmann and Rey 1987). Cor- <br />relation of biological data from otoliths with en- <br />vironml~ntal factors such as water temperature, riv- <br />er discharge, food availability, and predator abun- <br />dance bas elucidated mechanisms that control <br />growth. survival, and recruitment of early life <br />stages of fish (Crecco and Savoy 1985; Houde <br />1987; Rice et aI. 1987). <br />Uses of otolith data in biological investigations <br />accelerated after Pannella (1971) discovered daily <br />otolith growth increments. Subsequent research in- <br />dicated that increment formation and otolith <br />growth rates are influenced by photoperiod, water <br />temperature, diel water te~ature fluctuations, <br />food abundance, somatic growth rate, and meta- <br />bolic rates (Taubert and C6ble 1977; Campana and <br />NeiIsOCl1985; Secor and Dean 1989, 1992). More- <br />over, rhythmic environmental events such as pho- <br />toperiod and diel temperature shifts may entrain <br /> <br />~ <br /> <br />1 Corresponding author: <br />kbestgen@picea.cnr.colostate.edu <br /> <br />an endogenous endocrine-driven circadian rhythm <br />that controls daily increment deposition and otolith <br />growth (Campana and Neilson 1985; Secor and <br />Dean 1992). Although otolith growth and somatic <br />growth (used in this paper to mean increase in body <br />length) generally are positively correlated (Cam- <br />pana and Neilson 1985), the assumption of closely <br />proportional growth may be flawed because otolith <br />growth sometimes is consistent during periods of <br />variable somatic growth (Mosegaard et aI. 1988; <br />Reznick et al. 1989; Secor and Dean 1989; Wright <br />et al. 1990; Francis et aI. 1993). This "growth rate <br />effect" may invalidate some back-calculations of <br />fish length based on proportional otolith and so- <br />matic growth (Campana 1990). Species-specific <br />validation of increment deposition and otolith <br />growth patterns-defined by Francis (1995) as es- <br />timating the accuracy of determination methods- <br />is critical because of the many factors that affect <br />otolith microstructure. <br />Here, we report on effects of environmental con- <br />ditions on daily increment formation and otolith <br />growth in young Colorado squawfish Ptychochei- <br />Ius lucius, an endangered cyprinid endemic to the <br />Colorado River basin (Behnke and Benson 1983; <br />Tyus 1991). To determine if otoliths can be used <br />to describe age and growth of early life stages of <br />Colorado squawfish in the wild, we tested the fol- <br />lowing hypotheses: (1) increment deposition be- <br /> <br />105 <br />