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94
<br />MUTfI ET AL.
<br />The utility of external fluorescence produced by
<br />exposure to tetracycline as a mark for young fish
<br />appears limited by its relatively short time of reten-
<br />tion and detectability after treatment. Brothers
<br />(1985) reported observations similaz to ours for
<br />larvae and early juveniles of lake trout Salvelinus
<br />namaycush exposed to TC and suggested that the
<br />presence of external fluorescence after treatment is
<br />a good indicator of otolith marking success. Hettler
<br />(1984) noted that the head and fins of larval spot and
<br />pinfish preserved 8 d after immersion in OTC solu-
<br />tions ftuorescedyellow under longwave UV light. In
<br />mark-recapture studies of short duration in which
<br />larvae are released and sampled soon after marking,
<br />external fluorescence might permit identification of
<br />marked fish without sacrificing them.
<br />Specimen Preservation
<br />In this study, the otoliths removed from Colo-
<br />rado squawfish larvae that were fixed and pre-
<br />served in 95% ethanol (as recommended by
<br />>3rothers 1987) were in excellent condition, but
<br />the larvae themselves were shrunken and de-
<br />formed due to dehydration. Conversely, larvae
<br />that were fixed and preserved in formalin solu-
<br />tions buffered to pH 6.8 were in good morpholog-
<br />ical condition, but their otoliths were either disin-
<br />tegrated or were significantly degraded and use-
<br />less. The specific cause for loss or degradation of
<br />the otoliths is not known. Because the skeletal
<br />features of larvae preserved in formalin solutions
<br />buffered nearly to neutrality were successfully
<br />retained, we considered that 10°10 formalin fixative
<br />and 3% formalin preservative, both made with
<br />distilled water and buffered to pH 6.8 with phos-
<br />phate (Markle 1984), would be adequate for the
<br />preservation of otoliths. Perhaps alkaline formalin
<br />solutions (about pH 8.0) are required as suggested
<br />by Steedman (1976) and McMahon and Tash
<br />(1979), or water content in the solutions (greater
<br />than 96%'0) was too high (Steedman 1976), or both.
<br />Perhaps, calcium ion concentration in the preser-
<br />vative should have been near saturation rather than
<br />almost absent (as in solutions made with distilled
<br />water). For the present, although we prefer and
<br />recommend formalin solutions buffered nearly to
<br />neutrality for most other purposes, we can only
<br />follow other researchers and recommend that
<br />specimens be preserved in concentrated alcohol
<br />(e.g., 95% ethanol) or frozen for otolith analysis.
<br />Acknowledgments
<br />This study was funded under Federal Aid in
<br />Fish Restoration matching grant 02-O1-035 SE-3
<br />administrated through the Wildlife Research Unit,
<br />Colorado Division of Wildlife. We thank J. Hamill
<br />(U.S. Fish and Wildlife Service, Denver, Colo-
<br />rado) for arranging the required endangered spe-
<br />cies permits, R. Hamman (Dexter National Fish
<br />Hatchery, Dexter, New Mexico) for providing
<br />Colorado squawfish larvae, and D. Keefe (Envi-
<br />ronmental Research and Technology, Incorpo-
<br />rated, Fort Collins, Colorado) for providing fat-
<br />head minnow larvae. R. Behnke, C. Carlson, and
<br />D. Snyder reviewed earlier drafts.
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