NORTH AMERICAN SALMONIDAE 



237 



There are very few moi-phological characters 

 by which the various species can be unmistakably 

 identified because — 



1. The latitudinal range of many of the species 

 is so wide that the meristic character, which 

 usually show a latitudinal cline, are quite variable 

 for the same species in different localities (see 

 Mottley, 193-4a). 



2. For those species with fresh-water forms 

 there is a tendency for the geogi-aphically isolated 

 populations to develop slight differences. 



3. Anadromous and fresh-water dwelling fish 

 of the same population may show environmental 

 differences in form or coloration. Some of these 

 differences, especially color, have been shown by 

 Wilder (1952) to be reversible in Salvelimus 

 fontinalis. 



4. In fresh-water forms there may also be alti- 

 tudinal clines. In some instances, these seem to 

 involve retention of juvenile characteristics. For 

 example, the parr marks in the golden trout, 

 Salmo gairdneri agua-honita, and the piute trout, 

 Salm-o clarki seleniris (see Snyder, 1940). 



The foregoing does not mean that there are not 

 valid species. Any experienced fisherman has no 

 difficulty in separating the five species of Pacific 

 salmon at a glance, even though most individual 

 characters overlap in their range. Species are 

 recognized by a combination of characters and 

 most taxonomic descriptions encompass only a 

 few of those most readily taken and easiest to 

 reduce to numbers. 



ATTRIBUTES ANALYZED TO INDICATE 



RELATIONSHIPS 



HYBRIDIZATION 



One line of incjuii-y that yields a clue to inter- 

 relationships comes from hybridization experi- 

 ments. Within recent years several investigators 

 have obtained chromosome counts of salmonids 

 (table 1). In the few species studied, the diploid 

 number ranges from 60 to 84. Of course number 

 alone is not always the controlling factor. Thus, 

 in describing experiments with the crossing of 

 Saln^o mkir, S. fruffa, SaZvelinus alpiniis, and S. 

 fontinalis, Aim (1955) writes — 



The chromosomes of the Brown trout and the Char are, 

 in spite of being the same number, greatly differentiated 

 from one another and the former are more homologous 

 with those of the Salmon. The Brook trout and the Char 

 chromosomes are more in agreement with each other than 

 with the other .species. 



AUREOLUa^ ^ 



Figure 1. — Relative success of crossbreeding of Salmonl- 

 dae (except Oncorhynchus) . (Length of solid lines 

 shows relative success ; see table 2 ; dotted lines indicate 

 failure; arrows, direction of male-female cross.) 



In comparing Sahno gairdneri and S. salar 

 sehago. Buss and Wright (195G) noted that 

 "Bungenberg dejong has indicated (1955) a 

 marked difference in the chromosome structure of 

 these species. . . ." 



Table 1.- 



-Diploid chromo8ome numter in certain 

 Salmonidae 



From several sources we have compiled table 2 

 showing the results.of certain crosses between spe- 

 cies of Salmonidae {On^orht/nchiis is shown in a 

 separate table). To obtain a clearer view of the 

 results we have rated the success of each cross 

 from 1 to 6 (excellent to failure, see table 2). Al- 

 though this is subjective, it aids in studying the 

 results which are portrayed in figure 1. 



