CRESSEY ET AL.: COPEPODS AND SCOMBRID FISHES 



such as complete loss of vomerine teeth, these spe- 

 cies have diverged from the primitive condition. 



Gymnoaarda Gill 



The monotypic genus Gymnosarda differs from 

 other bonitos in a series of characters (Collette and 

 Chao 1975). The dogtooth tuna, G. unicolor (Riip- 

 pell), is a coral reef species of the tropical Indo-West 

 Pacific (Collette and Chao 1975:fig. 69). Its large 

 eyes and teeth, numerous olfactory lamellae, and 

 well- developed swim bladder indicate that it is more 

 of a lurking predator on larger fishes than are the 

 other bonitos. Copepod fauna: 3 species in 2 genera. 

 Each copepod species was found only once, so it is 

 difficult to draw any conclusions from the data. One 

 species, C. bonito, is characteristic of the Sardini. 

 Caligus productus is known from a wide variety of 

 hosts, both scombrid (14 species from all tribes ex- 

 cept Scombrini) and nonscombrid. Shiinoa occlusa is 

 otherwise restricted to Indo-West Pacific species 

 of Scomberomorini. 



Allothunnus Serventy 



The systematic position of this monotypic genus is 

 still in some doubt. It was included in the Sardini by 

 Collette and Chao (1975) because it lacked the spe- 

 cializations considered diagnostic of the Thunnini 

 and showed similarities to the bonitos in characters 

 such as the otoliths. It differs from all other scom- 

 brids in having the prootic bones remarkably extend- 

 ed laterally as wings that frame the posterior margin 

 of the orbit and in having a very large number of gill 

 rakers. A llothunnus resembles the Thunnini and dif- 

 fers from other Sardini in having a prootic pit in the 

 ventral surface of the skull. The pineal window is 

 large and oval in Allothunnus, elongate and slit- 

 shaped in the Thunnini and all other Sardini. The 

 liver has three subequal lobes as in the bluefin tuna 

 species group of Thunnus. Allothunnus fallai Serven- 

 ty is found around the world in the Southern Ocean 

 south of lat. 35°S (Collette and Chao 1975:fig. 69) 

 with one highly unusual record from the Los Angeles- 

 Long Beach harbor complex (Fitch and Craig 



1964). 



Copepod fauna: Elytrophora brachyptera was pres- 

 ent in all 5 Pacific specimens that we examined and 

 was also reported by Webb (1976) in 45 of 47 speci- 

 mens that they examined from Tasmania. This cope- 

 pod is otherwise known only from the tuna genus 

 Thunnus where we have found it in six of seven spe- 

 cies (all but T. tonggol). These copepod data support 

 a closer phylogenetic relationship betweenA//ot/iun- 



nus and Thunnus than was indicated by Collette and 

 Chao (1975). Two specimens from off the tip of South 

 Africa, however, carried the copepod C. bonito, a 

 common parasite of Sardini species. Infestation by C. 

 bonito can be viewed as primitive in Allothunnus; in- 

 festation by Elytrophora advanced. Sharing special- 

 ized morphological characters and copepod parasites 

 suggests that serious consideration must be given to 

 transferring A llothunnus from the Sardini to a posi- 

 tion as the most primitive member of the Thunnini. 

 This issue will be considered further by Collette. 



Thunnini 



The four genera of tunas are unique among bony 

 fishes in having countercurrent heat exchanger sys- 

 tems of rete mirabilia in the circulatory system. 

 These systems allow tunas to retain metabolic heat 

 so that the fish is warmer than the surrounding water. 

 The three more primitive genera (Auxis, Euthynnus, 

 and Katsuwonus) and the yellowfin tuna group of 

 Thunnus have central and lateral heat exchangers; 

 the specialized bluefin tuna group of Thunnus has 

 lost the central heat exchanger and has evolved well- 

 developed lateral heat exchangers (Carey et al. 1971; 

 Graham 1973, 1975). Copepod fauna: 17 species in 7 

 genera. Caligus coryphaenae, C. asymmetricus, and 

 C. productus were found on species in all four genera 

 of Thunnini. Caligus coryphaenae is common on the 

 body surface of seven species of Euthynnus, Kat- 

 suwonus, and Thunnus, and we have one record from 

 Auxis sp. (and one record from A canthocybium). It is 

 also common on species of the dolphin genus Cory- 

 phaena, a similarity we believe due to similarity of 

 epipelagic habits. Caligus productus was found on 20 

 species of scombrids, from all tribes except the 

 Scombrini. It occurred on 9 of the 13 species of Thun- 

 nini but was common (infestation 28-92%) on Kat- 

 suwonus and 3 species of Thunnus. Caligus 

 asymmetricus was also found on scombrids from all 

 tribes except the Scombrini, on a total of nine host 

 species. It appears to be more characteristic of the 

 Sardini, occurring commonly (infestation 8-12%) in 

 Cybiosarda and two species of Sarda, than of the 

 Thunnini (found in four species, infestation 1-7%). 

 One additional copepod, Pseudocycnus appendicula- 

 tus, is characteristic of Thunnini and occurs on 9 of 

 13 species, in all genera except Auxis. However, it is 

 common (infestation 14-27 %) in only three species of 

 Thunnus: T. tonggol, T. albacares, and T. maccoyii. 



Auxis Cuvier 



This is the most primitive genus of the Thunnini. 



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