116 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICK 



From these observations of gonads it may be 

 inferred that the big-eyed tuna also spawns in the 

 area south of the Caroline Islands. Partial veri- 

 fication of the existence of spawning grounds in 

 these waters is furnished by Marukawa (Hatai 

 et al. 1941), who reported at a gathering of 

 Japanese scientists convened to discuss tuna and 

 skipjack spawning that "Juveniles of big-eyed 

 tuna measui'ing 4.2 to 4.3 inches were found inside 

 yellowfin tuna taken by longlines in the Tokobei 

 area (Tobi Island, 3° N., 131°31' E.) last year, 

 while I was in Palau, by a ship of the Fisheries 

 Experiment Station.'" No mention is made, 

 how6ver,'of the date of capture. Despite cai-eful 

 search, juveniles of big-eyed tuna were not found 

 in the many stomachs of yellowfin tuna and other 

 jjelagic fishes examined aboard the mothership. 



Little is known of the spawning season of the 

 big-eyed tuna; observations, however, suggest 

 that it spawns from June to September, and pos- 

 sibly later. The possibility is not excluded that 

 spawning may be a year-round phenomenon. 



RECORDS OF JUVENILE OCEANIC 

 SKIPJACK (KATSUWONUS PELAMIS) 



While examining stomachs of fish landed 

 aboard the mothership, I recovered and preserved 

 in formalin seven juvenile scombroids later iden- 

 tified as oceanic skipjack, Katsuwonus -pelamis. 

 One specimen, measuring 130 mm. from the snout 

 to the end of the hypural plate, was found on 

 July 21, 1950, in the stomach of a black marlin 

 {Makaira masara) caught a few days previously 

 in the vicinity of 1°30' N., 154°08' E. Two addi- 

 tional juveniles of 132 mm. and 169 mm. were re- 

 covered on July 24, 1950, from a sailfish {Istio- 

 phoms orientalis) captured by longlines near 

 2°28' N., 155°01' E. The remaining four speci- 

 mens, measuring 81 nnn., 94 mm., 132 mm., and 

 148 mm., were found in stomachs of yellowfin 

 tuna {Neothunnus macroptemis) , the smaller two 

 on August 4, 1950, and the larger two on August 

 8, 1950. The earlier catches of yellowfin tuna 

 were made at approximately 1°10' N., 157°29' E., 

 and the later catches at 1°14' N., 157°28' E. Re- 

 mains of fish up to 250 mm. in size and identified 

 by skeletal characteristics as oceanic skipjack 

 were found in tunas and other pelagic fish but 

 were not retained because of their poor condition. 



All of the listed juveniles except the »i-iiii«i. 

 fish were X-rayed in the laboratories of the Pa- 

 cific Oceanic Fishery Investigations in Honolulu, 

 Hawaii. On negatives taken of these juvenile 

 scombroids the skeletal "trellis"' of Kishinouye 

 (1923) (="basketwork" of Godsil and Byers 

 (1944)) was faintly visible in every case and 

 placed these fish within Kishinouye's family 

 Katsuwonidae. The Katsuwonidae include two 

 genera : Euthynnus, which is composed of species 

 having either 37 or 39 vertebrae (Kishinouye 1923, 

 Schaefer and Marr 1948b), and Katsuvjonun, 

 which contains a single species characterized by 

 41 vertebrae (Kishinouye 1923). There is no 

 knowledge of an overlap in vertebral counts be- 

 tween genera. The total count of 41 vertebrae, 

 including the urostyle, therefore, specifically iden- 

 tified these juveniles as Katsuwonus pelamis 

 Linnaeus. 



For further verification, the 81-mm. juvenile 

 was stained, using HoUister's method (1934). 

 There are 41 vertebrae present with 20 precaudal 

 and 21 caudal vertebrae. The lateral processes on 

 the precaudal vertebrae are well developed and 

 the inferior foramina form a "trellis" with the 

 haemal arches. The haemal canal is large, and 

 the first closed haemal arch is on the twelfth ver- 

 tebra. The gill-raker count for the first gill arch 

 on the left side, which is 15 for the upper arch 

 and 38 for the lower, falls within the range of 

 counts given for adults — 15 to 20 and 36 to 38, 

 respectively (Kishinouye 1923). Palatine teeth 

 are present ; vomerine teeth are absent. Vestigial 

 palatine teeth were observed on the 94-mm. speci- 

 men and were absent on the next larger juvenile 

 of 130 mm., so that palatine teeth disappear at 

 a length somewhere between these two. 



The presence of juvenile oceanic skipjack in 

 stomachs of fish caught throughout the area fished 

 by vessels of the expedition points to the existence 

 of extensive spawning grounds in or adjacent to 

 these waters. The only previous published record 

 of juvenile skipjack from this general locality is 

 that of Inanami (1942). Since this reference is 

 not generally available, my translation of his paper 

 is given here in full : 



When I went to Truk in June of this year, I was shown 

 siiecimens of small skipjack at the Nanko Fishei'ies Com- 

 pany. Of tlie two, one specimen measuring over 6 sun 

 (180 mm.) was unmistakably a skipjack juvenile; the 

 other, measuring 1.5 »un (45 mm.) in length, may have 



