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<br />JUNE 2004
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<br />THE SOUTHWESTERN NATURALIST 49(2):203-208
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<br />COMPARISON OF FOUR TECHNIQUES FOR AGING ADULT COLORADO
<br />PIKEMINNOW, PTYCHOCHEILUS LUCIUS
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<br />LORRAINE A. HAWKINS, HAROLD M. TYus, * W. L. MINCKLEY, AND DAVID L. SCHULTZ
<br />
<br />Cooperative Institute Jor Research in Environmental Sciences, University oj Colorado at Boulder;
<br />Boulder; CO 80308-0216 (LAH, HMT)
<br />Present address oj LAH: Catty Marine Laboratory, Division oj Environmental and Evolutionary Biology,
<br />University oj St. Andrews, St. Andrews, FIFE, KY16 8B]>, Scotland
<br />Department oj Biology, Arizona State University, Tempe, AZ 85287-1501 (WL~Deceased)
<br />Department oj Biology, Nicholls State University, Thibodaux, LA 70310 (DLS)
<br />*Correspondent: harold. tyus@wlorado.edu
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<br />ABSTRACT-We estimated ages of Colorado pikeminnow, Ptychocheilus lucius, by counting annuli
<br />in scales, vertebral centra, whole otoliths, and thin otolith sections. Vertebrae provided the most
<br />precise estimator of age and the range of ages obtained were highly correlated with total length.
<br />Ages estimated from sectioned otoliths were ranked second in precision and strongly correlated
<br />with vertebral ages. Ages read from scales underestimated vertebral ages, 3;nd ages estimated from
<br />whole otoliths were most variable and least related to total length. Ages estimated using all 4
<br />structures from the same individuals revealed a close relationship between ages estimated with
<br />vertebrae and sectioned otoliths.
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<br />RESUMEN-Estimamos las edades de salmon blanco, Ptychocheilus lucius, contando anillos en es-
<br />camas, en la parte central de vertebras, en otolitos enteros, y en secciones finas de otolitos. Las
<br />vertebras proporcionaron el calculo mas preciso de la edad y el rango de edades obtenidas fue
<br />altamente correlacionado con la longitud total. Edades caIculadas de otoiitos seccionados fueron
<br />situadas en segundo lugar en precision y altamente correlacionadas con las edades vertebrales.
<br />Las edades obtenidas de escamas subestimaron las edades vertebrales, y edades estimadas de los
<br />otolitos enteros fueron mas variables y menos relacionadas a la longitud total. Las edades estimadas
<br />usanda las cuatro estructuras del mismo individuo revelaron una relacion cercana entre edades
<br />estimadas con vertebras y otolitos seccionados.
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<br />Fish ages are usually determined from the
<br />number of growth rings (annuli) present in
<br />some body structures. Scales have long been
<br />the standard aging structure because they are
<br />easy to retrieve, require no sophisticated prep-
<br />aration, and do not require the fish to be sac-
<br />rificed (Jearld, 1983). However, results from
<br />scale aging have been questioned because of
<br />several problems. Scales are subject to calcium
<br />reabsorption and regeneration, false annuli,
<br />and misreading (Carlander, 1987; Soupir et a!.,
<br />i9Y7; Long and Fisher, 2001).
<br />Otoliths and vertebrae are harder and more
<br />permanent structures that-also are used for ag-
<br />ing fishes. They contain different chemical
<br />compositions than scales (Maisey, 1987), but
<br />also have periodic ring depositions that are an-
<br />nual in many species. In addition, spines, rays,
<br />opercles, cleithra, and other structures also
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<br />,
<br />have been used (Beamish and McFarlane,
<br />1987).
<br />Ages of Colorado pikeminnow, Ptychocheilus
<br />lucius, a federally-listed endangered fish en-
<br />demic to the Colorado River basin of the
<br />southwestern United States, have been esti-
<br />mated from scales with some conflicting results
<br />(Vanicek and Kramer, 1969; Seethaler, 1978;
<br />Hawkins, 1992). The accuracy of age'S' obtained
<br />from scales (adjusted for presumed miSSIng an-
<br />nuli) has been validated in Colorado pikemin-
<br />now of ages to 10 years by comparison with fish
<br />of a known age (Hawkins, 1992). However, ag-
<br />ing of older Colorado pikeminnow, which his-
<br />torically reached sizes up t6 1.8 m total length
<br />(TL) (Miller, 1961) and potenu1uly ages of 50
<br />years, has been hampered by one or more
<br />missing annuli in young fish, indiscernible an-
<br />nuli, and a lack of age validation for older fish
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