FISHERY BULLETIN: VOL. 81, NO. 2 



Differences from the more advanced three genera of 

 Thunnini were summarized by Collette (1979). 

 Copepod fauna: 6 species in 2 genera, Unicolax and 

 Caligus. The two species of Unicolax are shared with 

 several species of Sardini and with species of Euthyn- 

 nus in the Thunnini. Euthynnus is the genus most 

 closely related to Auxis. Three of the species of Cal- 

 igus are also found in the other three genera of Thun- 

 nini. The fourth, C. pelamydis, is shared only with 

 Euthynnus among the Thunnini, but parasitizes 

 scombrids in the other three tribes, particularly the 

 Sardini. We have not found P. appendiculatus on 

 Auxis, but it is known from species in the other three 

 genera of Thunnini. Thus, infestation of copepods 

 clearly relates Auxis to the other Thunnini, par- 

 ticularly Euthynnus. 



There are two species of frigate mackerels (Fitch 

 and Roedel 1963): The narrow-corseleted A. tha- 

 zard (Lacepede) and the wide-corseleted A. rochei 

 (Risso). The two species have been clearly distin- 

 guished in the Pacific by Kishinouye (1923), Wade 

 (1949), and Matsumoto (1960) under a variety of 

 names. Both species are widely distributed in tropi- 

 cal and subtropical waters of the Indo-Pacific, and 

 both species apparently also occur in the Atlantic 

 (Richards and Randall 1967). Confusion in identi- 

 fication of many specimens dictates that we refer all 

 our copepod records for the genus to Auxis sp. Fri- 

 gate mackerels are the smallest of the tunas, A. ro- 

 chei reaching 600 mm FL and A. thazard at least 

 420 mm. 



Euthynnus Lutken in Jordan and Gilbert 



Euthynnus is closely related to both the more primi- 

 tive^ uxis and the more advanced Katsuwonus. Some 

 workers (Fraser-Brunner 1950; Collette and Gibbs 

 1963) have placed the monotypic Katsuwonus in syn- 

 onymy with Euthynnus, but this obscures the rela- 

 tionships of Euthynnus sensu stricto with Auxis and 

 of Katsuwonus with Thunnus. Euthynnus differs 

 from Auxis in having a common trunk for the dorsal 

 and ventral branches of the cutaneous artery. It is 

 less advanced than Katsuwonus because the ventral 

 branch of the cutaneous artery is short and dendritic 

 (Godsil 1954), much less developed than the dorsal 

 branch. The dorsal cutaneous artery lies dorsal to the 

 corresponding vein in Euthynnus, not ventral as in 

 Auxis. Collette (1979) has summarized the generic 

 differences along the genera of Thunnini. Copepod 

 fauna: 11 species in 4 genera. Three species of 

 Caligus (asymmetricus , pelamydis, productus) and P. 

 appendiculatus are widespread among the Thunnini. 

 Two species of Unicolax (collateralis and myc- 



terobius) are shared only with Auxis in the Thunnini 

 but also with species of Sardini. Caligus bonito was 

 found on all three species of Euthynnus but is most 

 commonly found on members of the tribe Sardini. 



There are three allopatric species of Euthynnus: E. 

 alletteratus (Rafinesque) in the Atlantic; E. affinis 

 (Cantor) throughout the Indo-West Pacific; and E. 

 lineatus Kishinouye in the eastern Pacific. There is a 

 valid record of E. affinis from the eastern Pacific 

 (Godsil 1954:139) and two of E. lineatus from the 

 Hawaiian Islands (Matsumoto and Kang 1967; Ma- 

 tsumoto 1967). Godsil (1954: table 17) has sum- 

 marized the characters that differentiate the species 

 (with£. affinis asE. yaito). Two bomolochid and one 

 caligid copepod parasites of Euthynnus apparently 

 show host specificity within the genus. Unicolax 

 anonymous is known only from the nasal sinuses of E. 

 alletteratus in both the eastern and western Atlantic. 

 Ceratocolax euthynni is also restricted to the Atlantic, 

 but occurs on Sarda sarda as well. Caligus regalis is 

 restricted to E. affinis (and Grammatorcynus in the 

 Scomberomorini) and may replace the closely re- 

 lated, more widespread C. coryphaenae on this host. 



Katsuwonus Kishinouye 



This monotypic genus is related to both Euthynnus 

 and Thunnus, and is more advanced than Euthynnus. 

 The generic characters of Katsuwonus are sum- 

 marized by Collette (1979). The skipjack tuna, Kat- 

 suwonus pelamis (Linnaeus), is a moderate-sized 

 tuna, about a meter long and weighs 18 kg, rarely 

 more than 23 kg. It has the highest number of gill 

 rakers of any of the Thunnini, 53-63 on the first arch. 

 It is cosmopolitan in tropical and subtropical seas. 

 Copepod fauna: 6 species in 3 genera. The three 

 species of Caligus and P. appendiculatus are wide- 

 spread among species of Thunnini. The fifth cope- 

 pod, U. reductus, is a highly specialized species re- 

 stricted to Katsuwonus. It appears to replace the 

 more primitive U. collateralis, U. mycterobius, and 

 U. anonymous, which are common in the nasal si- 

 nuses of the two more primitive genera of Thunni- 

 ni, Auxis and Euthynnus. This copepod evidence 

 tends to support recognition of Katsuwonus as a 

 separate genus. 



Thunnus South 



This, the most advanced genus of Scombridae, con- 

 tains seven species. Posterior to the corselet, the 

 body is covered with small scales but is naked in 

 other genera of Thunnini. A swim bladder is present 

 in all the species except T tonggol. Vertebral trellis- 



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