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resulted in a high perCent return in 1980, but it is not known if the dimin- ishing percentage after the second year is due to differential mortality or mark loss, however, the latter is suspected. Control bass marked in 1981 showed a 75% mark retention during the first year following spraying. Trends for percent composition of marked fish should become more evident with several more years of sampling and results from control group retention. Table 2. Proportion of stocked largemouth in each age-class captured by electrofishing in Chatfield Reservoir, Colorado. Sample % and (no.) represented in each age-class a year 1 2 3 4 1979 10(30) 1980 94(172)b 12(17) 1981 54 (95) 59 (53) 10(3) 1982 96 (41)b 59 (21) 26(9) 9 (2) a . . Flgures are not adJusted for mark loss. b Stocked fish not dispersed before sampling. At this point, the contribution of stocked bass can best be assessed when the fish are age II. By their second year in the reservoir they have dis- persed and mark loss will be at a minimum. If this is the case, then bass stocked in 1979, 1980, and 1981 comprised 12%, 59%, and 59% of all bass in their year-class, respectively. An estimation of year-class strengths can be extrapolated from the data in Tables 1 and 2. For instance, the contribution of marked bass at age II in 1981 and 1982 were both 59%. However, from Table 1, numbers of bass stocked in 1981 were about three times greater than in 1980. From this, it is assumed that the natural 1980 year-class was also three times larger than the 1979 year-class. There was a question concerning the ability of stocked bass to survive in a natural system, particularly after being raised primarily on an artificial diet. In all years, stocked bass were smaller than natural bass of a corres- ponding age-class by 8-20 rom (Table 3). By age II, however, the stocked bass were larger than their naturally produced counterparts. This size difference averaged 19 rom. Fieldhouse (1971) also found that stocked bass which were smaller than native at stocking reached a size attained by natural fish in later years. Even though stocked bass gained most of their growth on artificial diets while at the hatchery, they did not appear naive when presented natural foods in the form of forage fish. The bass readily took minnows during the fall and winter, and overwinter mortality was usually less than 10%. -I 57