<^ 



k 



(Q) 



Figure 2.— Outlines of corselets drawn from actual specimens 

 (Jones 1963). (a) Auxia rochei; (b) A. thnzard - typical short- 

 corseletted condition; (c) A. thazard - intermediate condition. 



Among internal characters that have been a source of 

 confusion is the gill raker count. Wade (1949) and Herre 

 and Herald (1951) pointed out that A. thazard in the 

 western Pacific normally have fewer gill rakers than A. 

 rochei. And A. thazard taken in the eastern Pacific and 

 the Indian Ocean also have counts that are definitely 

 lower (Mead 1951; Jones 1963). Godsil (1954), on the 



other hand, reported that all the A. thazard taken off 

 Baja California and the Galapagos Islands have high gill 

 raker counts similar to those reported for A. rochei by 

 Wade (1949) and Herre and Herald (1951). Matsumoto 

 (1959), however, believed that the number of gill rakers, 

 by itself, is not a reliable character in identifying the two 

 species of Auxis. But Jones and Silas (1964) suggested 

 that the gill raker counts could be useful; in case of 

 doubtful identification from external characters, a com- 

 bination of gill raker counts and corselet width should 

 facilitate specific identity. 



Jones and Silas (1964) have used body cross section as 

 an aid to identification but CoUette and Gibbs (1963a) 

 have warned that this character is difficult to use (Fig. 

 3). Also suggested by Jones and Silas was the position of 

 the visceral organs (Fig. 4). Godsil (1954) and Yoshida 

 and Nakamura (1965) noted that other prominant dif- 

 ferences between the two species occur in the skeletal 

 structure. In A. thazard, the temporal crests diverge an- 

 teriorly so that they are not parallel to one another (Fig. 

 5) and the width of the skull is wider in relation to body 

 length (Fig. 6). Yoshida and Nakamura also noted that 

 the length of the anterior branch of the haemal processes 

 was longer and touching on the preceding arch of the 

 24th to the 28th vertebrae in A. thazard (Fig. 7). 



1.33 Protein specificity 



Taniguchi and Nakamura (1970) examined muscle 

 protein of A. thazard and A. rochei by the cellulose 

 acetate electrophoretic method to determine whether 

 specific divergence occurred between species. They 

 found five components in the electropherograms of both 

 species, but some components were not common to both. 

 The genus Auxis, they concluded, contains two distinct 

 species based on external and internal morphological 

 characters although they are closely related. 



To analyze muscle protein polymorphism in Auxis col- 

 lected from the coastal region of Kochi Prefecture, 

 Japan, Taniguchi and Konishi (1971) used starch-gel 

 electrophoresis and detected differences in protein 

 specificity between A. thazard and A. rochei. They con- 

 cluded that whereas no individual variation could be rec- 

 ognized in electropherograms of 11 specimens of A. 



Table 4. — Comparison of gill raker counts for 84 Auxis thazard from three geographical 

 localities (Fitch and Roedel 1963). 



'On all specimens the center raker has roots extending into both limbs. 



