CRESSEY ET AL.: COPEPODS AND SCOMBRID FISHES 



copepod species are occasional parasites of non- 

 scorabrid hosts. 



The distribution of infestation rates on scombrid 

 hosts for these three species is summarized below. 

 Caligus bonito is apparently most common on species 

 of Sardini and is only an occasional parasite of Atlan- 

 tic Scomberomorus and Grammatorcynus and with 

 scattered records from Thunnini (mostly western 

 Atlantic and eastern Pacific). 



Caligus mutabilis is apparently restricted to the 

 western Atlantic, and its most common scombrid 

 hosts are species of Scomberomorus. As in the case of 

 C. productus in the Atlantic, this copepod probably 

 replaces the Indo-Pacific species of Caligus, more 

 host-specific to Indo-Pacific Scomberomorus. 



Caligus infestans has been recorded primarily from 

 iS. commerson from the Indian Ocean and eastward as 

 far as Indonesia. Although its preferred host ranges 

 north to Japan and east to Fiji, C. infestans apparent- 

 ly is replaced in these areas by C. cybii, host-specific 

 to Indo-West Pacific Scomberomorus. Kabata (1965) 

 reported C. infestans from Euthynnus alletteratus 

 {— affinis) from queensland, and Heller (1865) ori- 

 ginally described this species from Scomber from 

 Java. The second author believes the latter host to be 

 incorrect and the host was probably Rastrelliger. 

 Four literature records and five additional collec- 

 tions reported by Cressey and Cressey (1980) indi- 

 cate that S. commerson is undoubtedly its preferred 

 scombrid host. 



Caligus pelamydis and C. cybii are, together with C. 

 coryphaenae and C. regalis, the most primitive of the 

 10 species considered here (assuming a 3-segmented 

 fourth leg exopod is primitive to a 2-segmented one). 

 Caligus pelamydis has been reported many times 

 (Margolis et al. 1975; Cressey and Cressey 1980) pri- 

 marily from Sarda sarda (usually reported as Pela- 

 mys sarda or Gymnosarda pelamys) and Scomber 

 scombrus. Although our recent collections indicate 

 Sarda species as a frequent host, several other litera- 

 ture records from Scomber scombrus may indicate 

 that this fish is a more common host than our collec- 

 tions indicate. Most literature records are from Euro- 

 pean waters, whereas most of the S. scombrus we 

 examined were from the western Atlantic. Possibly 

 this copepod is more common on European S. scom- 

 brus than on American specimens. In addition, C. 

 pelamydis has been reported from Euthynnus, Auxis, 

 and Scomberomorus niphonius. 



It is interesting to note that C. pelamydis is a com- 

 mon parasite of S. niphonius, whereas its close rela- 

 tive, C. cybii, is reported from six other Indo-West 

 Pacific species of Scomberomorus. It seems likely 

 that C. pelamydis is more primitive than C. cybii. This 



suggests that S. niphonius is the most primitive spe- 

 cies of Indo-West Pacific Scomberomorus. The 

 ranges of both C. cybii and C. pelamydis overlap in 

 Japan (C. cybii from S. koreanus, 11 of 19 fish infest- 

 ed). Caligus cybii apparently evolved parasitizing 

 species of Indo-West Pacific Scomberomorus other 

 than S. niphonius. 



The closely related C. coryphaenae and C. regalis 

 are both found on the body surface of their hosts. 

 Consequently, the data may be biased because much 

 of the host material used for this study is preserved in 

 museum collections, and body-surface copepods, for 

 the most part, are no longer present. Most of the 

 specimens of Thunnini, however, were examined in 

 the field, and infestation rate data are more reliable. 

 Because C. coryphaenae is ubiquitous (circumglobal 

 distribution and on many different species of hosts), 

 it can be presumed to be more primitive than C. 

 regalis (restricted to the Indian Ocean and south- 

 western Pacific and found only on E. affinis and 

 Grammatorcynus). Caligus coryphaenae is also com- 

 mon on Coryphaena hippurus and C. equiselis. Within 

 the Scombridae, both species are primarily parasites 

 of the Thunnini with scattered records on Scom- 

 beromorini (Acanthocybium and Grammatorcynus). 

 Caligus regalis, previously known only from E. affi- 

 nis, has recently been collected by the first author 

 from three specimens of G. bicarinatus from Aus- 

 tralia. This is within the known geographic range of 

 the parasite, but is another example of copepod para- 

 sites shared by the Scomberomorini and the Thun- 

 nini. 



Within each of the four groups of Caligus with more 

 than one species discussed here, one species of 

 Caligus is widely distributed (circumglobal in three 

 cases) and the remaining species are much more re- 

 stricted in distribution (Figs. 9-12). 



In conclusion, analysis of the collection data for the 

 10 species of Caligus considered here suggest the 

 following: 



1. Although Caligus species are generally not re- 

 stricted to one host, they are often confined to a genus, 

 tribe, or family and, in all cases considered here, they 

 show strong host preferences at a generic or specific 

 level. For example, although C. productus is found on 

 three of the four tribes of Scombridae, it has sig- 

 nificantly higher rates of infestation on Katsuwonus 

 and Thunnus within the Thunnini. Caligus bonito is 

 recorded from three tribes of scombrids but is much 

 more common on the tribe Sardini. 



2. Within each group of related Caligus parasitic on 

 scombrids, one species is either circumglobal or is 

 significantly more widespread than any others. 



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