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'1jrsa~it1 , METHODS AND MATERIALS Wild rainbow trout have been spawned in the Colorado River every spring since 1981. Annual egg-takes from this operation have ranged between 40,000 and 80,000. Eggs have been incubated, hatched, and reared 'to fingerling size at four different hatcheries over the past 6 years; however, for the past 4 years, the eggs have been taken to the Bellvue Research Hatchery and Roaring Judy rearing units. Progeny from the Research Hatchery are being used to establish a brood stock of the Colorado River rainbows (CRR). With the expansion of the study rivers from one (the Rio Grande) to four, including the Animas, Blue, and upper Gunnison rivers, the decision was made to use a strain of rainbow referred to as the Tasmanian rainbow (TAS) in conjunction with the Colorado River rainbow (CRR) as an additional study species. While the overall objective of the study is to establish "wild", rainbow populations in the four study rivers,a sub-objective of the study,is to determine if a domesticated hatchery rainbow strain, such as the TAS, will per~orm equally well over the long-term in natural stream environments, or does a truly wild CRR strain outperform all other rainbow strains., Since we know that TAS rainbows ,worked very well in the Fryingpan River (Nehring,l987), the decision was made to use the TAS strain'as the "domestic" fingerling rainbow stock in this experiment. Population estimates are made once each year to evaluate the growth and survival of the, CRR ,and TAS rainbow plants, as well as the density and biomass of the resident brown trout populations. Boat electroshocking techniques are employed on the large rivers in the study (Animas, upper Gunnison, and Rio Grande rivers) while walk shocking techniques are used on the smaller Blue River. Since none of the four study streams have an endemic rainbow populations, all rainbow stocks are of hatchery origin. The annual plants of rainbow fingerlings are separated on the basis of different fin clips and age/growth analysis using scale reading and back-calculated length analyses. Table,S contains,the,Animas River stocking history information by ,study' section, species, numbers, sizes, marks, and stocking date. The Blue River received two plants of rsinbow fingerlings in late August, early September 1987. The plants consisted of 9,000 CRR rainbows from the Fish Research Hatchery that averaged 5 cm (1. 97 in.) in size, were unmarked, and planted August 3lst. The Blue River was also stocked with 25,000 TAS strain rainbow fingerlings that were marked with an adipose fin-clip. These fingerlings averaged 8.38 cm (3.3 in.) in size and were also planted on August 3lst. All fingerlings were point stocked out of the hatchery trucks. I 00002398