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.. 266 to the body wall by connective tissue and bound by adhesions. Encapsulated transmitters were at- tached to scar tissue of the old incision in several fish. No transmitter was free in the body cavity. Encapsulation of these transmitters appears nor- mal because encapsulation and fibrous tissue fix- ation is considered a normal body response to for- eign objects as the body seeks to isolate them (Swanson 1969). Movement of foreign material implants, is a common problem in reconstructive surgery (Cal- nan 1963). Transmitter coatings such as silicone (Malette and Eiseman 1965) or silicone rubber (Swanson 1969) are not very tissue reactive and may permit implant movement through the body. Immobilization of implants with these coatings may be accomplished by placing them under lig- aments, tendons, or fascia (Swanson 1969). Move- ment and loss of transmitters ,through body tissue as noted by Summerfelt and Mosier (1984), Chis- holm and Hubert (1985), and Marty and Sum- merfelt (1986) are not desirable. The use of bees- wax as a transmitter coating (Tyus and McAda 1984; Tyus et al. 1987) may have contributed to the retention of implants recovered in this study. Mild tissue irritation and resultant connective tis- sue growth around (and possibly into) the beeswax and polystyrene capsules in this study hindered migration and expulsion of the capsules. Marty and Summerfelt (1986) found that small- er weights of dummy transmitters resulted in a significant decrease in expulsion rate and recom- mended a transmitter weight less than 2% of the fish's weight. Mesing and Wicker (1986) and Mil- ler and Menzel (1986) achieved long-term trans- mitter retention with a transmitter-to-fish weight ratio of less than 1.5%. My results corroborate these findings; transmitter weights averaged less than 1 % in implanted Colorado squawfish and ra- zorback sucker. Effects of implanted transmitters on fish growth were evaluated by comparison of growth rates be- tween recaptured implanted and recaptured non- implanted fish. Growth of 14 recaptured Colorado squawfish (size range, 482-770 mm) implanted with transmitters (mean, 11.2 mm/year; SD = 10.2) was no different (Student's t = 0.3; P = 0.76) than that of 59 nonimplanted dangler-tagged fish in the same size range (mean, 10.2 mm/year; SD = 11.3). Average growth rate of 2 razorback suckers (2.5 mm/year) from which implants were removed was similar to that of 39 nonimplanted fish (2.2 mm/ year). Retention of transmitters had no discernible long-term effect on growth of these individuals. 1 1 I , TYUS Recapture rates for Colorado squawfish (26%; N = 70) and razorback sucker (22%; N = 9) im- planted with transmitters in the Green River com- pared favorably with those for nonimplanted, dan- gler-tagged fish: 16% (N = 336) for Colorado squawfish and 19% (N = 323) for razorback sucker. Comparison of these implant and tag return ratios suggests that long-term differential mortality due to the surgical implants was no different from that experienced with dangler tags. (Lower catch rates of dangler-tagged fish may be related to tag loss.) The results of this study agree with those of Minor (1981), who reported no mortality or change in behavior in five surgically implanted fish species. Mellas and Haynes (1985) noted a 33% loss of surgically tagged trout but attributed the loss to stress-related effects of holding them 24 h before release. Stasko and Pincock (1977) concluded that implanted fish should be released soon after sur- gery to minimize stress to the fish. Although trans- mitter expulsion has not been conclusively linked with holding stress, it may be so related. Acknowledgments This study was supported by funds provided by the Bureau of Reclamation, and Fish and Wildlife Service, U.S. Department of the Interior. P. B. Holden, R. A. Valdez, and R. D. Williams fur- nished information on radios they implanted or retrieved. Many biologists with the Colorado Riv- er Fishes Project aided in radiotelemetry and fish sampling. K. M. Paulin aided in data retrieval and analysis. P. H. Eschmeyer, R. C. Summerfelt, J. M. Haynes, and two anonymous reviewers pro- vided review comments on an early version of the manuscript. W. L. Minckley furnished encourage- ment and many helpful suggestions. References Calnan, J. 1963. The use of inert plastic material in reconstructive surgery. British Journal of Plastic Surgery 16:1-22. Chisholm,!. M., and W. A. Hubert. 1985. Expulsion of dummy transmitters by rainbow trout. Trans- actions ofthe American Fisheries Society 114:766- 767. Holden, P. B., and D. A. Selby. 1978. A study to de- termine the spawning requirements of Colorado squawfish. Report (Contract 14-16-0009-77-050) to U.S. Fish and Wildlife Service, Logan, Utah. Malette, W. G., an B. Eiseman. 1965. Silicone in the prevention of intestinal adhesions. American Sur- geon 31 :336-338. Marty, G. D., and R. C. Summerfelt. 1986. Pathways and mechanisms for expulsion of surgically-im- planted dummy transmitters from channel catfish.