FRESHWATER FISH FAUNA 191 



(Ostariophysi = Cypriniformcs) containing about 5,000 species. 

 Also of value are the secondary (II) freshwater fishes representing 

 groups largely restricted to fresh water but salt-tolerant and capable 

 of occasionally crossing narrow sea barriers. The remaining fishes 

 known from fresh water may be divided as follows (Myers, 1938, 

 1951) : Diadromous (III), those that regularly migrate between fresh 

 and salt water during a definite period of the life cycle. Vicarious 

 (IV), essentially or presumably non-diadromous freshwater repre- 

 sentatives of partly or primarily marine groups. Complementary 

 (V), species that are often or usually diadromous and belong to 

 marine groups that become dominant in fresh waters only in the 

 scarcity or absence of primary and secondary fishes. Sporadic (VI), 

 fishes living and breeding more or less indifferently in salt or fresh 

 water or entering fresh water only sporadically. The 30 families 

 recorded from fresh water within the area comprise 6 primary 

 groups with nearly 100 species and 3 secondary families with only 15 

 species. Thus the primary (I) and secondary (II) fishes constitute 

 somewhat more than half the total number of species that occur in 

 western fresh waters. 



The absence of a large and diverse drainage system, such as the 

 Mississippi, and the general scarcity and instability of the aquatic 

 environment help to explain why the freshwater fish fauna of the 

 West lacks many of the families and genera, especially lowland types, 

 that live east of the Rockies (Fig. 1). The depauperate western fauna 

 comprises only half as many families and one-fourth as many species 

 of primary and secondary fishes as the eastern fauna. It is made up 

 of relicts, an abundance of monotypic genera, and a complex of 

 endemic faunas with few widespread species in common. Many of 

 the species are of restricted distribution (Fig. 2). 



Our knowledge of the systematics of this fish fauna is behind 

 that of the other vertebrates. This is especially true of the published 

 record. Although the few taxonomists who have worked with western 

 fishes in the past quarter century have restricted most of their 

 publication to the description of new taxa, I estimate that about 10 

 per cent of the species have yet to be described. Rather considerable 

 recent field work, begun in 1934, has built up a wealth of preserved 

 material and observations that await critical evaluation. No up-to- 

 date generic revisions have appeared, and the inadequate fossil 

 record provides few hints for speculation on the interrelationships of 



