Striped marlin (Fig. 4) 



In specimens under 4 mm in total length, the ptero- 

 tic spine is inclined very slightly upward from the 

 base, but with growth of the larvae, it runs very 

 nearly parallel to the body axis. Thus the spine tip 

 does not extend beyond the body profile as in other 

 species. The preopercular spine is inclined sharply 

 downward, forming a large angle with the body axis. 

 The spine is nearly parallel to a line which might be 

 drawn along the edges of the upper and lower jaws. 



In order to facilitate comparison of the spines in 

 the different species, schematic drawings of head 

 profiles of the four species were prepared (Fig. 5). 



USE OF THE SPINES 

 AS DIAGNOSTIC CHARACTERS 



The larvae of sailfish and shortbill spearfish can be 

 identified reliably on the basis of pigmentation on the 

 lower jaw or on the branchiostegal membrane and 



■%*•>? 



Figure 3. — Larvae of shortbill spearfish, Tetrapturus an- 

 gustirostris. Top to bottom: 3.6, 5.5, and 8.6 mm in total 

 length. 



Figure 4. — Larvae of striped marlin, Tetrapturus audax. 

 Top to bottom: 4.1, 5.6, and 8.9 mm in total length. 



therefore identification of these species need not 

 depend on supplementary characters such as spines. 

 In the case of the blue marlin and striped marlin, 

 however, supplementary diagnostic characters are 

 essential in order that these species may be identified 

 without error. The spine characteristics are particu- 

 larly useful in differentiating the very small larvae, 

 especially of blue and striped marlin smaller than 

 7 mm. 



As mentioned previously, there are occasional 

 specimens of sailfish larvae whose head profile very 

 closely resemble that of striped marlin larvae. In 

 these cases, also, the use of the supplementary 

 characters will prevent errors in identification. 



Although both the pterotic and preopercular 

 spines tend to "degenerate" after the larvae attain a 

 certain size, and thus become less useful as diagnos- 

 tic characters, there are fortunately other characters 

 which can be used effectively in the identification of 

 larger specimens. The spines are thus useful and 



75 



