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Population size can be calculated using the following formula (Lande and. Barrowclough 1987): NN = Number of Nales N' _ (NM + NO NF Number of Females Estimating effective population size is complicated. For example, the formula given above for the effect of sex ratios assumes random mating, constant population size through time, and variance in fertility that approaches Poisson distribution. Effective population size can be maximized by non-random matings of paired individuals and equalizing the sizes of family lots (Allendorf 1993). The effective population size should be maximized in every hatchery generation to reduce the loss of genetic variation (Kapuscinski et al. 1993). Strategies for conserving genetic diversity are summarized in Box 9. If N is known, the rate of inbreeding ( F) can be calculated using the formula: 1 F = 2 N By applying this formula, the estimated rate of inbreeding for an effective population size of 50 (equal sexes) is 1 %. For an effective population size of 10 (equal sexes), the estimated rate of inbreeding is 5%. Therefore, it is advantageous to use as many adult fish as possible in developing broodstocks. Box 9. Strategies for conserving genetic diversity of listed and candidate fish. 1. Genetic diversity of wild fish stocks should be characterized by genetic markers. 2. Captive propagation and stocking should be considered temporary management tools to facilitate development of self-sustaining wild fish stocks. 3. Wild broods sources are preferable and captive broodstocks should be developed from an appropriate donor source. 4. Appropriate breeding strategies should be used to maintain genetic diversity similar to the wild donor stock or population. 5. Genetic diversity of captive broodstocks and their progeny will be monitored and compared to the genetic diversity of wild stocks. 6. The number of captive-reared fish stocked should be limited to prevent genetic swamping of severely depleted wild stocks. 20 •