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trays until hatching (96 to 168 hours post-fertilization}, then moved to holding tanks until <br />swim-up (approximately seven days post-hatch). Egg production per female ("fecundity") is <br />determined gravimetrically. Embryo viability (used as an estimator of expected hatch) is <br />assessed at 48 hours post-fertilization. Actual larval production is measured by water <br />displacement after hatching is complete. <br />Isolation and analysis of mtDNA.- Hatchery-produced razorback suckers were characterized <br />by restriction endonuclease analysis of mtDNA samples from three year classes (1987, 1989, <br />and 1990) using the enzymes described above. Composite haplotypes for each individual are <br />provided in Table 2 and Appendix I. <br />Statistical analysis.- Levels of genetic diversity within year classes were estimated as <br />described above. Significance of differences in h values among source and hatchery samples <br />was tested by randomly resampling the data (computer program modified by TED from <br />HAPLOID of Weir, 1990). A distribution of diversity values was generated by drawing 1000 <br />random samples of 10 individuals from the source population represented by our sample of 25 <br />individuals from Lake Mohave, and calculating diversity for each. Sampling of an individual <br />was followed immediately by its replacement; individuals could therefore be selected several <br />times or not at all in each replication. Mean diversity value for each set of 1000 resamples <br />and its 95% confidence interval were obtained from the distribution of diversity values (Weir, <br />1990). <br />Effect of broodstock size on h was also examined by computer simulation. The above <br />program was modified to sample a highly diverse source population (ranging from 2 to 100 <br />individuals, with each individual possessing a different haplotype) to generate 10,000 progeny. <br />Progeny haplotypes were obtained by randomly sampling parental haplotypes (with <br />replacement as described above). From this "hatchery stock," 1000 samples of 14 individuals <br />18 <br />