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MANAGEMENT BRIEFS 849 factory for this purpose. Blood, scales, and epi- dermis have been investigated for nonlethal use (e,g" Carmichael et at 1986; Whitmore et at 1992), but without investigation of chronic effects on the fish, Scales would appear to be ideal for use as noninvasive tissue retrieval, but there are drawbacks, Scales are mostly bone, not all species have scales, and some species have scales that are small or embedded, Sampling of mucus has similar problems and removal of scales and mucus from a large area may also cause harm (e,g., infection), Scales and mucus may have diminished protein diversity (Morizot et al. 1990), which may require a large sample, and both tissues are susceptible to contamination by water-borne chemicals or ge- netic material of epizootic organisms, Further- more, they may require extensive and specialized preparation (e,g" Herzberg 1978), Sex products, such as oocytes, can also be obtained with little injury to the fish, but obtaining these may be dif- ficult because spawning individuals must be lo- cated when they are ripe and nonlethal samples are difficult to take from immature fish, Finally, contaminants and stable isotopic assays may re- quire the use of certain tissues because chemical substances tend to be differentially concentrated in various organs (Newman 1998), The effects of invasive tissue sampling have been studied for only a few economically impor- tant species (e,g" Harvey et al. 1984; Morizot et al. 1990), and nonlethal invasive sampling has not been widely used to obtain tissue for analytical work, presumably due to a lack of acceptable pro- tocols, However, a variety of tissues are valuable for biochemical assays, including muscle, liver, and fin. Muscle is a good source of metallic chem- icals (Newman 1998), stable isotopes (Hesslein et at 1991, 1993; Angradi 1994), and DNA (Buth 1984; Morizot et al. 1990), Muscle biopsies of salmonids and catostomids appear to cause little mortality (Crawford et al. 1977; Seeb et al. 1986, Waddell and May 1995), Liver has been monitored (e,g" for changes in gross morphology and changes in hepatic parenchymal cells) because it is susceptible to damage from a variety of toxi- cants, Damage to hepatic tissue has been the most frequently reported effect in fishes exposed to var- ious chemical agents (Gingench 1982; Newman 1998), Thus, liver has been widely used for his- tological examination (Gingench 1982; Newman 1998), contaminants analyses (Pokras et al. 1998), stable isotopic studies (Hesslein et al. 1993), and genetic characterization (Carmichael et al. 1986; Hillis et al. 1996), However, liver tissue samples are difficult to remove from live fish, and liver biopsy of largemouth bass resulted in 20% mor- tality (Harvey et al. 1984), Fin tissue can be used for genetic determinations (Carmichael et al. 1986) and may potentially be valuable for other assays as well. Most marking studies indicate little or no mortality associated with fin-clipping, although re- moval of a substantial portion of a fin can decrease growth and survival by affecting fish movements (Wydoski and Emery 1983), As valuable as tissue analysis may be, its use in threatened or endangered fishes poses a dilem- ma: recovery efforts often would benefit from in- formation gained from tissue analysis, but the nec- essary information may only become available by risking some of the few remaining fish, Not only are there very few individuals available for sam- pling, but fishes listed under the Endangered Spe- cies Act (ESA) are protected from harm by federal and state statutes, The only option available in the past has been the sacrifice of a few individuals, With a small sample size, there is concern that those few individuals may not be representative of the population, A nonlethal tissue sampling pro- cedure would be especially valuable for rare, threatened, endangered, or other valuable fishes, We performed controlled experiments to eval- uate acute and chronic effects of invasive tissue sampling for removing muscle, liver, and fin tissue from three fish species, each from a different fam- ily, Rainbow trout Oncorhynchus mykiss (Salmon- idae) were used for developing techniques that were then applied to two federally endangered spe- cies, razorback sucker Xyrauchen texanus (Cato- stomidae) and bony tail chub Gila elegans (Cy- prinidae), This study was commissioned by the U,S, Fish and Wildlife Service (USFWS) with the goal of developing an invasive tissue sampling protocol for endangered fishes, for a variety of purposes, Development of a successful protocol for acquiring necessary tissues with minimumal harm to the fish (Le" a very low mortality rate) would enable USFWS to issue ESA research per- mits for collecting information needed to support ongoing recovery efforts, Methods Tissue samples and surgical procedures,-We designed experiments to evaluate the effects of tissue removal on fish survival and growth of three fish species, each representing a different family, Hatchery-reared rainbow trout were used to de- velop and refine techniques, and the resulting pro- tocol was then applied to endangered razorback