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September 1989 Notes 435
<br />In this study, the TC marking technique described by Muth et al. (1988) for 5-day-old (posthatching)
<br />larvae of Colorado squawfish was successfully adapted to late embryos and newly hatched larvae of
<br />this species. Immersion in TC solutions did not affect egg-hatching success or fish survival, growth,
<br />and development, and all treated larvae examined had detectable amounts of TC deposited in their
<br />otoliths. The high fish mortality on day 4 posthatching for all experimental groups (including controls)
<br />occurred during the period of gas bladder inflation (swim-up, as defined by Blaxter, 1988). Swim-up
<br />is a potential "critical period" in the early development of fish larvae and high mortality may be
<br />expected (Blaxter, 1988). For best mark intensity, immersion in 200 to 350 mg TC/1 for 24 to 36 h
<br />is recommended For marking embryos and 350 mg TC/1 for 4 to 12 h for marking newly hatched
<br />larvae. Average mark-intensity values obtained in these experiments were similar to those reported by
<br />Muth et al. (1988) for the same TC exposures and sampling times. Results of this study and those
<br />reported by Muth et al. (1988) demonstrated that Colorado squawfish larvae can be successfully marked
<br />as late embryos or recently hatched larvae by TC marking of otoliths. Which early-life interval one
<br />selects for TC marking depends on the objectives of the mark-recapture study and, if hatchery-produced
<br />eggs or larvae are used, their availability. Advantages of embryo marking are that eggs are easier to
<br />work with than larvae during treatment and that after treatment, eggs can be placed in the river
<br />substrate where larvae can hatch and disperse naturally.
<br />The TC marking technique possesses many of the attributes of an ideal marking method reported
<br />by Laird and Stott (1978). Muth et al. (1988) concluded that TC marking of otoliths met their
<br />requirements for an optimal mark, i.e., mark must be applicable to late embryos or recently hatched
<br />larvae, suitable for mass marking in the field, innocuous, detectable for at least 8 weeks, and relatively
<br />easy and inexpensive to apply and detect. Availability of an effective mass-marking technique for
<br />Colorado squawfish larvae eliminates a preliminary obstacle for field mark-recapture experiments
<br />concerned with young-oF-the-year distribution, behavior, and survival during drift-dispersal and back-
<br />water-nursery periods. The recovery program for endangered fishes of the Upper Colorado River Basin
<br />is scheduled for completion within the next 15 years with the objective being recovery and delisting of
<br />the species. To accomplish this goal within the alloted timeframe, biologists working on these Rshes
<br />need to conduct experimental studies relating specifically to applied management and recovery. We
<br />believe that mark-recapture studies on age-0 Colorado squawfish, like those proposed by the CDOW,
<br />could effectively address high-priority research needs concerned with reproduction and early life history,
<br />especially young-of-the-year survival and recruitment.
<br />This study was funded under Federal Aid in Fish Restoration matching grant 02-01-035 SE-3
<br />administrated through the Wildlife Research Unit, Colorado Division of Wildlife. We thank J. Hamill
<br />far arranging the required endangered species permits and R. Hammon for providing Colorado squaw-
<br />fish eggs. We also thank K. Bestgen, S. Platania, and J. Piccolo for their assistance. This paper is
<br />contribution no. 40 of the Colorado State University Larval Fish Laboratory.
<br />LITERATURE CITED
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<br />XI, Part A: The physiology of developing fish-eggs and larvae (W. S. Hoar and D. J.
<br />Randall, eds.). Academic Press, New York, 546 pp.
<br />BROTHERS, E .B. 1987. Methodological approaches to the examination of otoliths in aging studies.
<br />Pp. 319-330, in Age and growth of fish (R. C. Summerfelt and G. E. Hall, eds.). Iowa State
<br />Univ. Press, Ames, 544 pp.
<br />HAMMAN, R. L. 1986. Induced spawning of hatchery-reared Colorado squawfish. Progressive Fish-
<br />Culturist, 48:72-74.
<br />HETTLER, W. F. 1984. Marking otoliths by immersion of marine fish larvae in tetracycline. Trans.
<br />Amer. Fish. Soc., 113:370-373.
<br />LAIRD, L. M., AND B. STOTT. 1978. Marking and tagging. Second ed. Internatl. Biological Programme
<br />Handb., 3:84-100.
<br />MOTH, R. T., T. P. NESLER, AND A. F. WASOWICZ. 1988. Marking cyprinid larvae with tetracycline.
<br />Amer. Fish. Soc. Symp., 5:89-95.
<br />NESLER, T. P., R. T. Mu'rH, ANn A. F. WASOWICZ. 1988. Evidence for baseline Row spikes as
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