By Dr. Harry Specht
Copyright by Dr. Harry Specht, 1996
The subject of genetic diversity in fish was explored in detail by Gary Sutcliff’s article, “Preserving Genetic Diversity in Killifish Species Maintenance,” in JAKA, Vol. 23, 1992. In the article, he provided data which indicated that the minimum effective breeding population to preserve the maximum amount of the native gene pool should consist of 6 to 10 individuals, or five pairs.
Genetic drift, or the loss of genes, occurs with each generation. Increasing the minimum population increases heterozygosity, or genetic diversity, and reduces the rate of loss. Assuming a base breeding pool of 10 individuals, the first generation offspring will retain 95% of the original genetic diversity. After five generations, only 77.4% of this original genetic material remains.
Gary’s is a most interesting and informative article, which can be utilized to set forth a practical long range species maintenance program.
Start with as many fish as possible, with a minimum of five pairs. If possible, start with wild fish for heterozygosity, or secure fish from different sources for a diverse gene pool.
Breed every fish in the group, using random selection to determine pairing. Cull fry only for obvious defects.
Separate the eggs from each pairing and select 4-6 fry from each spawn for breeding the next generation. With problem species it is advisable to raise the fry from each spawn separately until they sex out, then select a male and a female from each for breeding.
Breeding for all succeeding generations should involve a minimum of five pairs of fish.
This procedure is being followed, roughly speaking, by the Killifish Conservation Committee of the AKA. The coordinators select representative species (Core Species), and then appoint a Keeper of the Studbook for each species to record the genetic background of the founding fish. Next it is necessary to find a number of aquarists willing to maintain those Core species. Upon direction of the Keeper of the Studbook, exchanges are made among the members maintaining a species, to assure maximum genetic diversity. This is the model for genetic diversity being followed by zoos all over the world as they cooperate in breeding their captive stock.
This conservation activity is just commencing in the AKA, in an effort to prevent genetic drift among our captive populations of killifish. It is apparent that many killifish species are being lost in nature and that a number of species are now found only in captive populations, such as Cyprinodon alvarezi and Cynolebias whitei. We
We hobbyists must make an effort to maintain our killifish, or many species will be lost forever. Insuring genetic diversity becomes vital with the loss of wild populations, as there may in the future be no wild fish to restore stocks or genetic diversity.
I would encourage anyone interested in conserving killifish to join the AKA, and to participate in the Killifish Conservation Committee.
— G.C.K.A. Newsletter, January 1997