brae is erroneous. First, no other report in the 

 literature shows a wahoo having between 23 

 and 31 precaudal vertebrae, as one would ex- 

 pect if these counts encompassed the actual 

 range of variation ; instead, the number of pre- 

 caudal vertebrae has always been cited as 31, 

 32, or 33 when it was referable to a particular 

 specimen. Second, I found that six adult wahoo 

 taken during a cruise of the Charles H. Gilbert 

 to the southwestern Pacific in 1963 had either 

 31 or 32 precaudal vertebrae and 30 to 33 caudal 

 vertebrae (table 2). Six juvenile specimens 

 from other sources had 31 to 33 precaudal and 

 30 to 33 caudal vertebrae. 



Although the number of vertebrae may vary 

 slightly more in wahoo than in tunas, the varia- 

 tion is less than Kishinouye (1923) reported. 

 The vertebral formula for wahoo can be re- 

 stated as 31 to 33 -4- 30 to 34 -^ 62 to 66 ; the 

 most typical formula is 32 + 31 = 63. 



Other adult characters that are useful for 

 identifying young wahoo are the number of 

 spines and rays in the dorsal and anal fins. 

 Varying counts have been given for these 

 characters, also. Different authors have re- 

 ported 24 to 26 first dorsal spines, except 

 Jenkins (1904) who reported 27 (table 2). 

 Each of four adult wahoo that I examined had 

 27 first dorsal spines, but the last 2 were greatly 

 reduced and were buried beneath the skin and 

 muscle tissue. Although it was relatively easy 

 to locate the 26th spine by probing, it was ex- 

 tremely difficult to locate the 27th even with 

 careful dissection of skin and musculature. This 

 difficulty may account for the generally lower 

 spine counts reported previously for the first 

 dorsal fin. Three juvenile wahoo that I exam- 

 ined, including the specimen previously re- 

 ported by Strasburg (1964) as having 26 

 spines, also had 27 first dorsal spines. The last 

 spine was extremely small and appeared almost 

 to be the first spine in the second dorsal fin. 

 The number of spines in the first dorsal fin of 

 the wahoo thus appears to be constant at 27. 



The number of rays seems to vary slightly in 

 the second dorsal (12 to 14) and anal fins (12 

 to 13). The counts of 11 rays for both fins in 

 all of Kishinouye's reports and 11 rays for the 

 second dorsal fin reported in Cuvier and Valen- 



ciennes (1831: table 2) may be too low (by 

 error), or may represent extreme variations. 



In adult wahoo the dorsal and anal finlets 

 appear to be constant at 9, although Robert H. 

 Gibbs, Jr. (personal communication) found the 

 number to vary between 7 and 9 in 16 speci- 

 mens he examined. While preparing the skele- 

 tal material for the present study, I observed 

 that the posteriormost dorsal finlet and the 

 posteriormost anal finlet, which appeared to be 

 perfectly formed single finlets, were actually 

 composed of two separate finlets that had be- 

 come fused. The extra finlet is clearly reflected 

 in the total ray and finlet counts of the three 

 smallest wahoo (table 2). In both dorsal and 

 anal series the number of elements is generally 

 larger than the combined ray and finlet number 

 of the adults. 



DESCRIPTION AND DEVELOPMENT OF 

 LARVAL AND JUVENILE WAHOO 



Identification of wahoo larvae is simplified 

 because it is a single species (Lutken, 1880; 

 Jordan and Evermann, 1905; Beaufort and 

 Chapman, 1951 ; Collette and Gibbs, 1963) and 

 therefore the problem of differentiating mor- 

 phologically similar species is eliminated. The 

 larval characteristics described and illustrated 

 in this paper were obtained from specimens 

 that had been preserved in 10 percent Formalin 

 for many years and were sometimes based on 

 single specimens. The description, therefore, 

 may diflfer slightly from that of newly caught 

 specimens. 



Larval wahoo less than 3.4 mm. SL are read- 

 ily recognized by several characteristics: (1) 

 the large number of body segments in relation 

 to body length; (2) the elongate viscera; and 

 (3) the presence of one or two black pigment 

 spots on the ventral surface of the caudal 

 peduncle, similar to those on larvae of skipjack 

 tuna {Katsuwonus pclamis) . Larvae as small 

 as 2.8 mm. have 63 to 65 body segments, in- 

 cluding the urostyle (compared with 42 to 43 

 segments in skipjack), and the viscera extend 

 well over one-half the body length. Larvae 

 above 4.4 mm. can be recognized by the large 

 number of body segments, the extent of the 

 viscera (over two-thirds the body length), and 



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U.S. FISH AND WILDLIFE SERVICE 



