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~"~ u.~h~' l`'le.. isv~.er ®~ Reprinted from TxE Sov~rxwESTSxrr NA~i•axni.isT Vol. 40, No. 2, June 1995 Made in United States ofAmerica r MARKING OTOLITHS IN RAZORBACK SUCKER EMBRYOS AND LARVAE WITH FLUORESCENT CHEMICALS ROBERT T. MUTH AND STEVEN M. MEISMER Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, CO 80523 Efforts to recover the endangered razorback sucker (Xyrauchen texanus) include hatchery propagation of fish for reintroduction and re- search projects, documentation of reproduction and recruitment in the wild, and evaluation of reasons for low recruitment and ways to improve survival of young fish. Minckley et al. (1991) recommended marking hatchery-produced razor- back sucker to distinguish them from fish pro- duced naturally. Because razorback sucker are sometimes stocked in large numbers as larvae or small juveniles, amass-marking technique ap- plicable to early life stages is required. The mark- t ing technique could also be used in field mark- recapture studies to facilitate investigation of the early biology of razorback sucker and fate of re- introduced fish. Marking otoliths of fish has great potential for use in stock identification, assessment of stocking success, and life-history studies (Brothers, 1990; Buckley and Blankenship, 1990). One technique for rapid mass marking is incorporation of fluo- rescent chemicals in otoliths by immersion of fish embryos or larvae in solutions of these chemicals. Two compounds proven effective for this tech- nique are alizarin complexone (ALC) and tet-