8121

• UCREFRP Catalog Number: 8121
• Author: Williamson, J. H. and R. S. Wydoski.
• Title: Genetics Management Guidelines.
• USFW Year: 1994.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

encountered problems when the rate of inbreeding was 1% or lower per
generation. However, some animal breeders will allow inbreeding to
increase between 2% and 3%. A maximum of 1% in the inbreeding rate is
recommended for wild populations (Simberloff 1988). The acceptability of
the "500" value was proposed for genetic drift based on one trait in a
fruit fly. Both values of this "50/500" rule have been disputed and no
magic numbers or specific rules appear to be valid for propagation of
animals (Simberloff 1988). Inbreeding is of particular importance
because it has been demonstrated that a consequence of inbreeding
depression in brother-sister matings for some species will result in
offspring that are sterile or inviable after several generations (Lande
1988). The 1% maximum inbreeding rate recommended by Simberloff (1988)
for wild populations should be used as a target for an effective
population size in developing broodstocks of the endangered Colorado
River fishes.
Allendorf (1993) recommended stocking equal numbers of offspring of
family lots from pedigreed matings. This practice will reduce the
potential for loss of genetic diversity. Philipp et al. (1993)
recommended that genetic characterization of captive-reared fish be
compared with wild stocks to ensure that the genetic diversity is
similar.
I. Ideal Number of Founders for Broodstock Development. The designation of
"endangered" to any organism under the Endangered Species Act implies
that the numbers of wild organisms are limited. The basic goal in an
captive propagation program is to maintain the genetic diversity of
captive broodstocks that is similar to the parent wild stock. Simberloff
(1988) emphasized that general agreement does not exist about the
absolute numbers of animals needed to maintain genetic diversity in
captive propagation programs.
To achieve Simberloff's recommendation of keeping the maximum rate of
inbreeding at 1% or lower, an effective population size of fifty parents
(25 males and 25 females) is needed for development of a broodstock.
Mating of one male with one female is desirable to maximize the genetic
contribution from all fish used as parents (Allendorf 1993). This
strategy of 25 paired matings is recommended as a target for an effective
population size in the captive propagation of endangered Colorado River
fishes. This strategy was designated as "Priority 1" in Box 10 for the
maximization of genetic diversity in broodstock development. The
fertilized eggs from mating one male and one female (i.e., 1 family lot)
should be divided and reared in separate facilities to avoid the total
loss of the genetic contribution from those two parents through an
accident or catastrophe.
It is desirable to mate the 25 pairs of endangered fish in one year
because broodstocks would mature at the same time so that equal numbers
of all family lots could be produced and stocked from parents of the same
age. This procedure would eliminate many variables that could influence
genetic diversity and stocking success.
If sufficient numbers of endangered fish are in the wild, the goal would
be to increase wild recruitment until self-sustaining populations are
realized to meet the carrying capacity of available habitat. However,
for declining endangered fish stocks with little or no recruitment,
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