MORPHOLOGY AND DISTRIBUTION OF LARVAL WAHOO 



ACANTHOCYBIUM SOLANDRI (CUVIER) 



IN THE CENTRAL PACIFIC OCEAN 



B> Walter M. Matsumoto, Fishery Biologist 

 Bureau of Commercial Fisheries Biological Laboratory, Honolulu, Hawaii 96812 



ABSTRACT 



Descriptions are presented of the early developmental 

 stages of the wahoo, Acanthocybium solandri (Cuvier), 

 ranging from 2.8 to 23.7 mm. in standard length. Develop- 

 mental changes in body pigmentation, body form, fin 

 formation, and ossification of bones and other hard parts 

 were studied for 38 larvae collected in the central Pacific 

 Ocean. Drawings of larvae at various sizes are included. 

 Certain adult characters are discussed, such as: the number 

 of vertebrae and the vertebral formula; the number of 



spines and rays in the first dorsal, second dorsal, and anal 

 fins; and the number of dorsal and anal finlets. 



Larval and adult wahoo live in the open ocean as well as 

 near land. The adults spawn throughout the tropical and 

 subtropical waters between lat. 30° N. and 25° S. The 

 species spawns throughout the year in the equatorial waters 

 between lat. 14 N. and 15° S., and during the northern 

 and southern summer in areas farther from the Equator. 



Although considerable knowledge has been 

 gained in recent years about the early life his- 

 tory of the commercially important mackerels 

 and tunas, the larval and juvenile stages of 

 many scombroid fishes are poorly know^n. This 

 is particularly true of the larvae of the wahoo, 

 AcantJiocybium solandri (Cuvier). The smal- 

 lest wahoo previously recorded was a 23.7-mm. 

 juvenile from the central Pacific Ocean (Stras- 

 burg, 1964). Prior to this record, the only 

 mention of a young wahoo in the literature was 

 a 28-cm. juvenile caught off Japan in 1917 

 (Kishinouye, 1923). 



The wahoo, a member of the Scombridae, is 

 usually taken in small quantities as incidental 

 catches on the longline, and in larger quantities 

 by surface trolling (Iversen and Yoshida, 

 1957). It is found in tropical and subtropical 

 areas of the oceans. 



While sampling for tuna larvae in the central 

 Pacific Ocean from 1950 to 1962, the Bureau 

 of Commercial Fisheries Biological Laboratory, 

 Honolulu, Hawaii, collected 38 young wahoo 

 from 2.8 to 17.8 mm. SL (standard length) in 

 plankton net hauls. The morphology and dis- 



Published October 1967 



tribution of the larvae were studied to increase 

 our knowledge of the early life history of the 

 scombroid fishes. 



This paper describes the developmental 

 changes in body pigmentation, fin formation, 

 and ossification of various bones. It also dis- 

 cusses certain adult characters that require 

 definition, such as the number of vertebrae and 

 the vertebral formula, the number of spines 

 and rays in the dorsal and anal fins, and the 

 number of finlets. The growth rates of various 

 body parts are included, as well as new in- 

 formation on distribution of the species in the 

 central Pacific Ocean, as determined from 

 captures of the larvae and adults. 



COLLECTION AND TREATMENT 

 OF MATERIAL 



Plankton hauls were made with a 1-m. plank- 

 ton net on 32 cruises of the Bureau of Com- 

 mercial Fisheries research vessels Hiigh M. 

 Smith and Charles H. Gilbert from May 1950 

 to July 1962. The types of hauls varied slightly 

 over the years; generally, the net was hauled 

 obliquely from a depth of 200 m. to the surface 

 before 1956, but from 1956 to 1962, it was 



FISHERY BULLETIN: VOLUME 66, NO. 2 



299 



