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l? 1 1 1 11 1 1 1 1 Box 10. Recommended strategies to maximize the effective population size in the artificial propagation of endangered Colorado River fishes. These recommendations are in priority order. 1. Mate one male with one female as a minimally accepted protocol if wild adults are available until an effective population size of 50 is achieved to maximize the genetic contribution from the wild stock. 2. Breed as many adults as feasible in a given year until an effective population size of 50 is reached by mating one male with one female. If 25 families cannot be obtained during one spawning season, continue in the following years until 25 paired matings have been attained. 3. If numbers of adult endangered fish are low, use the 5 X 5 breeding matrix or di-allele cross to develop a broodstock (Figure 3). The half-sib family lots provide a safeguard against the potential catastrophic loss of the genetic contribution from any parents. 4. When wild fish are extremely rare and represented by unequal sexes, use factorial matings to capture the genetic contribution from all fish of the least numerous sex. For example, if three males and one female were available, three family lots should be produced by mating all three males with the single female. 5. Additional wild adults should be obtained to supplement the genetic contribution from the wild stock for broodstocks developed from the di-allele cross or factorial cross. Family lots from mating one male with one female should replace half-sib family lots to maximize the genetic contribution from the wild stock. ?l Endangered Fish are Available. If the number of available adult wild fish is low, mating 5 males and 5 females using a 5 X 5 breeding matrix (Figure 4) is reasonable (Item 3 in Box 10). Biology Committee participants and an Ad Hoc panel of fishery geneticists agreed that the 5 X 5 breeding matrix should be used as the basic minimal breeding strategy model for propagation of the endangered Colorado River fishes when the number of wild adults is limited. This model, the di-allele cross (Figure 4), involves mating 5 males with 5 females of a stock as broodstock founders to produce 25 family lots (Kapuscinski et al. 1993). The entire genetic contribution from mating 5 males and 5 females are represented in the diagonal cells (upper left to lower right). The remaining 20 crosses are various combinations of the parent genotypes. Pedigreed matings of this nature (a single uniquely-marked male mated with a single uniquely-marked female) ensure that every possible genotype is produced and each parent is genetically represented in the next generation, thus preserving allelic diversity in the offspring of the captive stock (Kapuscinski et al. 1993). The mating of ten unrelated 1 35