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... ." ,... 146 Conservation Biology of Fishes relationships. Some African rift lakes have "species flocks" consisting of over 300 described endemic spe- cies (references in Echelle & Kornfield 1984). How- ever, two morphologically distinct sympatric 'species' of cichlids endemic to Cuatro Cienegas, Mexico, have been shown to belong to a single reproductive popula- tion (Kornfield et aI. 1982). In addition, laboratory ex- periments with cichlids have shown that changing their diet can result in large differences in morphology (Meyer 1987). Fishes also show the greatest variety of reproductive systems among the vertebrates. Modes of reproduction in fishes include oviparity, viviparity, ovoviviparity, and ovi-ovoviviparity (Moyle & Cech 1982). Sexuality in fishes also runs the gamut of possibilities: simultaneous hermaphroditism, consecutive hermaphroditism, uni. sexuality, and bisexuality (Price 1986). Modes of sex determination in fish species includes male heterogam- ety, female heterogamety, multiple sex chromosomes, polygenic determination, single gene determination, and environmental determination (Price 1986). The genetic systems of fishes show similar diversity. Most fish species show normal diploid Mendelian inher- itance. However, alternative genetic systems in fish spe- cies include triploidy, tetraploidy, gynogenesis, and hy- bridogenesis (Turner 1984). Some of these alternative genetic systems also occur in amphibians and reptiles but they are more restricted in those taxa. For example, all of the described polyploid amphibian and reptilian species have closely related diploid counterparts, and no higher polyploid taxa have been found (Bogart 1980). Tetraploidy among fish taxa is much more wide- spread (Schultz 1980). Two of the more successful fam- ilies of fishes apparently are descended from their own tetraploid ancestor: catostomids (suckers: 12 genera, 58 species; Nelson 1976) and salmonids (salmon, trout, char, whitefish, and grayling: 9 genera, 68 species; Nel- son 1976). This diversity in reproduction and genetics is of more than academic interest. The paper in this issue by Allen- dorf & Leary ( 1988) discusses several unusual problems associated with the conservation of cutthroat trout. Many of the conservation problems with this salmonid species apparently result from its polyploid ancestry (e.g., fertile hybrids between taxa with large amounts of genetic divergence). Fishes are unique in that no other major food source of man is captured from wild populations. Nelson & Soule (1987) have considered this attribute of fishes in a philosophical context. The commercial harvesting of fish also has a variety of important biological implica- tions. Harvested fish populations are subjected to selec- tion on a variety of characteristics that affect an individ- ual's vulnerability to harvesting. Nelson and Soule (1987) have reviewed the evidence that differential har- vesting has caused genetic changes in fish stocks. Conservation Biology Volume 2, No.2, June 1988 ,411endotf The paper presented at the meeting by Nelson exam- ined this problem in detail in rockfish of the genus Se. bastes. This genus contains at least 100 species of ma- rine fish (Eschmeyer, Herald, & Hamman 1983); many of these species support important fisheries on the west coast of the United States. He concluded that our un- derstanding of the effects of exploitation cannot be gained by ordinary genetic methods. He recommended detailed analysis of the empirical effects of exploitation on the age schedule of growth and on changes in the size schedule of fecundity. The commercial and recreational value of fish popu- lations has also led to widespread culture of fishes in hatcheries for release into the wild to supplement nat- ural populations. There is no parallel among other taxa to the massive and continuous release of artificially cul- tured individuals over large areas such as became pos- sible through the development of hatchery programs in the last century (Allendorf, Ryman, & Utter 1987). For example, a single hatchery on Yellowstone lake col- lected and shipped over 818 million Yellowstone cut- throat trout (Salmo clarki bouvieri) eggs between 1899 and 1957 (Varley 1979)! A discussion of the need to protect fishes on their spawning grounds from an article on "pisciculture" by G. Brown Goode of the U.S. National Museum in the 1898 edition of the Encyclopedia Britannica presents the view of early fish biologists: How much must they be protected? Here the fish. culturist comes in with the proposition that "it is cheaper to make fish so plentiful by artificial means that every fisherman may take all he can catch than to en- force a code of protection laws." The salmon rivers of the Pacific slope of the United States, the shad rivers of the east, and the whitefish fish- eries of the lakes are now so thoroughly under control by the fish-culturist that it is doubtful if anyone will venture to contradict his assertion. The question is whether he can extend his domain to other species. It is interesting to note that two whitefish species from the Great lakes are extinct, and three additional species are threatened or endangered (Ono et aI. 1983). The paper by Allendorf & Leary (1988) discusses probta,ns in conservation related to artificial culture and relf>2S(: ofsalmonids throughout the western United Stat_, Fish are generally restricted to water. This obvious characteristic has some perhaps not so obvious effects on their conservation. For example, fishes are not as easy for humans to observe and appreciate as are birds and mammals. It has therdore been more difficult to attract public support for their conservation. Moreover, it also appears that fishes have been somewhat ignored by conservation biologists. For example, the most re- cent list of endangered and threatened species by the U.S. Department of the Interior (Federal Register 1987) includes over 300 species of mammals, over 200 species of birds, and only 83 species of fish, even though there