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review of the literature, we identified some method of otolith marking, as the approach which would most likely meet all of our requirements. Further, otolith marking fits nicely into our plans to develop otolith-ageing techniques for Colorado sq_uawfish larvae, since for most mark detection procedures the otolith must be removed from the fish and examined microscopically. Otoliths are the first calcified structures to appear in embryonic stages of most fish. Once formed, the early otolith growth structures remain intact and unchanged for the entire life of the fish (Brothers 1985). Tsukamoto (1985) considered otoliths to be the ideal structure for marking since they are in effect "biological internal tags". Because otoliths are the only permanent and persistent structures present in the very earliest life-history stages, they offer the only possibility for producing an endogenous and unique mark (Brothers 1985). Otolith marking for larval and juvenile fishes has been successfully accomplished by several techniques in a variety of fishes. Many of these observations and experiments were often included in studies of otolith growth, and were not intended to produce marked fish for release into the wild. Brothers (1985) provided an excellent review of otolith-marking techniques. The literature suggested at least four possible approaches to marking the otoliths of fish embryos and early larvae. The various methods require different treatments to produce the mark and different procedures for mark detection (Table 1--also included in Table 1 is a summary of procedures for staining fish larvae; staining procedures were considered initially, but were later rejected). The potential otolith-marking methods fell into the following categories (see Brothers 1985 for a complete discussion of each technique): 1. Microstructural patterns on otoliths produced by environmental maniuulations. Brothers (1981) observed that although light and feeding manipulations are possibilities, temperature manipulations produce the most reliable and striking results. Marks produced by temperature manipulations are clear and easily distinguishable with light microscopy. Analysis of the mark produced in this manner is quick and economical. 2. Chemical rarkers. A. Acetazolamide marking of otoliths. growth inhibitor and produces a mark disruption or interruption of growth. with light microscopy; however, mark the use of the scanning electron Preparation of the otoliths for SEM several detailed steps. Acetazolamide is a on the otoliths by Mark can be detected confirmation requires microscope (SEX). examination involves 3