After the larvae exceed about 8 mm, the pterotic 

 spine becomes shorter relative to body length, and 

 growth rate of the preopercular spine also decreases 

 with growth of the larvae. At a length of 1 1-12 mm, 

 these spines virtually stop growing and their lengths 

 relative to body length begin decreasing. 



DESCRIPTION OF THE PTEROTIC AND 

 PREOPERCULAR SPINES BY SPECIES 



The following is a brief description of the pterotic 

 and preopercular spines in the larvae of the Indo- 

 Pacific billfishes. Black marlin, M. indica, is omitted 

 due to lack of sufficient numbers of specimens. All 

 descriptions are of the lateral aspect of the larvae. 



Blue marlin (Fig. 1) 



The pterotic spine rises obliquely from its base. In 

 specimens larger than 4 mm, the spine tip extends 

 well beyond the dorsal profile of the larva. The 

 preopercular spine is slightly concave downwards 

 near its base but on the whole, it is very slightly 



concave upward. Viewing it from the side, it runs 

 very nearly parallel to the ventral profile of the larva. 



Sailfish (Fig. 2) 



The pterotic spine rises obliquely from its base. 

 The spine is relatively longer than in the larvae of 

 other species, and its tip extends markedly beyond 

 the dorsal profile. As in the blue marlin the preoper- 

 cular spine extends parallel to the body axis of the 

 larva but it is not as curved as in blue marlin. 



Shortbill spearfish, 



T. angustirostris (Fig. 3) 



Both the pterotic and preopercular spines are 

 shaped very similarly to those in the blue marlin. The 

 preopercular spine is, however, shorter than in blue 

 marlin and is also inclined further downward. Fur- 

 thermore, the secondary preopercular spines are 

 quite well developed in this species. 



*^s 



Figure 1. — Larvae of blue marlin, Makaira mazara. Top 

 to bottom: 3.5, 6.0, and 7.6 mm in total length. 



Figure 2. — Larvae of sailfish, Istiophorus platypterus . 

 Top to bottom: 4.2, 6.5. and 8.3 mm in total length. 



74 



