Abstract of Smith, G. R., J. Rosenfield, and J. Porterfield. 1995. Processes of origin and criteria for preservation of fish species. In Nielsen, J. L. (ed.), Evolution of the Aquatic Ecosystem, Defining Unique Units in Population Conservation. American Fisheries Society, Special Publication (in press).

Fish species are controlled by ecology more than by reproductive isolation. They originate via diverse processes; the result is individual lineages that do not all fit the same concept. Reproductive independence, morphological difference, and ecological specialization may occur in any order, creating different kinds of species, in their early stages. The irreplaceability of individuals (sensu Michael Ghiselin) is a unifying concept with systematic and conservation importance.