and there the number increases until a series 

 of melanophores forms over the entire base of 

 the anal fin. A similar series of melanophores 

 develops at the base of the second dorsal fin. 

 The only other significant increase in pigmenta- 

 tion is in the first dorsal fin just before the 

 larva reaches a length of about 13.0 mm. 



Premaxillary length, snout length less pre- 

 maxillary length, head length less snout, body 

 depth at anus, and snout-to-anus distance less 

 snout show allometric growth that can be de- 

 scribed by the equation, Y = bXa. 



The most striking change in body form occurs 

 in larvae longer than 3.8 mm., in which head 

 length increases very rapidly. Most of this 

 increase is due to the rapid growth in the pre- 

 maxillary and snout. The shape and size of 

 the mouth also are affected by the rapid growth 

 in premaxillary and snout. Prior to attain- 

 ment of 4.3 mm., both jaws have the same 

 length; subsequently, the upper jaw protrudes 

 beyond the lower, and at about 9.0 mm., the 

 ratio of upper to lower jaw is 1.25:1. This 

 ratio decreases to 1.07:1 in the 23.7-mm. juve- 

 nile, and in adults the upper jaw is equal to or 

 slightly shorter than the lower. Before unequal 

 jaw development begins, the ratios of upper 

 and lower jaws to head length is between 

 0.508:1 and 0.601:1. After their lengths be- 

 come unequal, the ratios of upper and lower 

 jaws to head length increase to 0.769:1 and 

 0.626:1, respectively. 



Body depth increases unevenly throughout 

 the size range. The most rapid growth occurs 

 in larvae between 9.0 and 9.2 mm. long. 



Snout-to-anus distance less snout length is 

 linearly related to standard length less snout 

 length. It increases 0.623 mm. for each milli- 

 meter increase in standard length less snout 

 length. 



Unlike the digestive tract of larvae of yellow- 

 fin tuna or skipjack tuna, which is compact 

 (anus located well ahead of the origin of the 

 anal fin), the digestive tract of wahoo larvae 

 is fully extended (anus located close to the ori- 

 gin of the anal fin). The digestive tract of wa- 

 hoo resembles that of yellowfin tuna and skip- 

 jack larvae in that it forms a complete loop. 



Orbit diameter is linearly related to stand- 



ard length. It increases 0.101 mm. for each 

 millimeter increase in standard length. 



Ossification of bones and hard parts differs 

 only slightly from the sequence found in jack 

 mackerel and Pacific mackerel. The sequence 

 in wahoo is as follows: Cleithrum and para- 

 sphenoid, maxillary and dentary, gill arches, 

 premaxillary, teeth of upper jaw, preopercular 

 spines, teeth of lower jaw, preopercle, articular, 

 palatine, vomer, palatine teeth, branchiostegal 

 rays, parietal, frontal, principal rays of caudal 

 fin, pectoral fin, second dorsal and anal fins 

 simultaneously, vertebrae, first dorsal fin, vom- 

 erine teeth, secondary caudal rays, pelvic fins, 

 opercle, and supraoccipital crest. 



Wahoo larvae were found in tropical and sub- 

 tropical waters between lat. 30° N. and 25° S., 

 and between long. 175° E. and 115° W., the 

 east-west extent of sampling along the Equator. 

 The numbers of lai'vae and adults caught in- 

 shore (less than 110 km. from land) and off- 

 shore were not significantly different. Wahoo 

 larvae were taken mostly during the summer 

 in the area north of lat. 15° N., and throughout 

 the year along the Equator between lat. 14° N., 

 and 15° S. 



ACKNOWLEDGMENTS 



Shoji Ueyanagi, of the Nankai Regional Fish- 

 eries Research Laboratory, Japan, sent me a 

 photostatic copy of Kishinouye's work (1908); 

 and Elbert H. Ahlstrom, Robert H. Gibbs, Jr., 

 Bruce B. Collette, and Frederick H. Berry 

 critically reviewed the manuscript. 



LITERATURE CITED 



Ahlstrom, Elbert H., and Orville P. Ball. 



1954. Description of eggs and larvae of jack 

 mackerel (Trachurus symmetricus) and distri- 

 bution and abundance of larvae in 1950 and 

 1951. Fish Wildl. Serv., Fish. Bull. 56: 209-245. 

 Allis, Edward P., Jr. 



1903. The skull and the cranial and first spinal 

 muscles and nerves in Scomber scomber. J. 

 Morphol. 18(2) : 45-326. 

 Beaufort, L. F. de, and W. M. Chapman. 



1951. The fishes of the Indo-Australian Archi- 

 pelago, IX Percomorphi (concluded) Blennoidea. 

 Leiden (E. J. Brill), xi -f 484 pp. 

 Berry, Frederick H. 



1964. Aspects of the development of the upper 

 jaw bones in teleosts. Copeia 1964(2): 375-384. 



320 



U.S. FISH AND WILDLIFE SERVICE 



