COPEPODS AND SCOMBRID FISHES: A STUDY IN 

 HOST-PARASITE RELATIONSHIPS 



Roger F. Cressey, 1 Bruce B. Collette, 2 and Joseph L. Russo 2 



ABSTRACT 



Host specificity of the copepods parasitic on scombrid fishes is the basis for an analysis of the host-parasite 

 relationship. A total of 46 different species of parasitic copepods were collected from 47 species of Scom- 

 brinae (the monotypic Gasterochismatinae is excluded). A revised host-parasite list is presented, including 

 new data by R. F. Cressey and H. B. Cressey. Those copepod species present on more than one host species 

 have preferred hosts, and indicate tendencies to being host specific. The copepods present an American 

 species of Scomberomorus suggest evolutionary trends in that group. Two species (ancestral S. cavalla and 

 ancestral S. sierra) were probably present prior to the separation of the Atlantic and Pacific Oceans. The 

 present Atlantic S. maculatus andS. brasiliensis arose from aS. sierra ancestor. Copepod data suggest that 

 the Indo-West Pacific S. eommerson is the most primitive extant species, while S. multiradiatus is the most 

 advanced. The copepods parasitic on Sarda species indicate the origin of that genus in Australasia, with the 

 Atlantic S. sarda being the most advanced species. The genus Allothunnus, previously regarded as a member 

 of the tribe Sardini, is shown to have affinities with the Thunnini and may be the most primitive member of 

 that tribe. A cladistic analysis of the copepod genus Unkolax correlates well with current hypotheses of the 

 phytogeny of scombrid genera. Host-parasite relationships of the Scombrinae are compared with those 

 found in a previous study of host-parasite relationships in needlefishes (Belonidae). Parasite- based host 

 phytogenies follow the methods of Brooks. 



In this paper we test the validity and application of 

 several parasitological theories regarding host-para- 

 site relationships of copepods parasitic on scombrid 

 fishes. As in our earlier joint effort (Cressey and 

 Collette 1970), in which we treated the relationships 

 of parasitic copepods and needlefishes, the analyses 

 are enhanced by the collaboration of specialists re- 

 presenting each animal group (Cressey — parasitic 

 copepods, Collette and Russo — scombrid fishes). 

 Parasite taxonomy on which the present paper is 

 based has been published separately (Cressey and 

 Cressey 1980). Additional material collected since 

 that publication and an updated list of hosts and 

 copepods, because over 200 additional scombrids 

 have been examined, are included in this paper. 

 Examples of 10 genera of copepods are illustrated 

 (Fig. 1) to indicate the kinds of copepods that para- 

 sitize scombrids. 



Because many earlier reports on parasitic copepods 

 contain misidentifications of both host and para- 

 site, we rely on our own collections or direct examina- 

 tion of specimens used in published accounts. 



The often repeated "Fahrenholz rule" (Noble and 

 Noble 1973:548) suggests that related parasites 



'National Museum of Natural History, Smithsonian Institution, 

 Washington, DC 20560. 



2 Systematics Laboratory, National Marine Fisheries Service, 

 NOAA, Smithsonian Institution, Washington, DC 20560. 



Manuscript accepted August 1982. 

 FISHERY BULLETIN: VOL. 81, NO. 2, 1983. 



are found on related hosts, thus indicating host phy- 

 logeny. This generalization we now know is an 

 oversimplification. 



Hennig (1966:109-110) illustrated how it is pos- 

 sible to have the same parasite species on hosts of 

 polyphyletic origin through incomplete parallelism. 

 Cautions on the use of parasites as indicators of host 

 phylogeny, echoed by Mayr (1957), Hennig (1966), 

 Noble and Noble (1973), and others, are well-found- 

 ed. We feel, however, that these problems can be 

 minimized by studying comprehensive collections of 

 both hosts and parasites, using the maximum num- 

 ber of parasite groups on the hosts. Presence of 

 parasites on any host may reflect host ecology, 

 chorology, or phylogeny. We believe that information 

 on host-parasite phylogeny has increased validity as 

 sample size, and the numbers of parasite species 

 from different parasite groups (Crustacea, Trema- 

 toda, Protozoa, etc.) available for study increases. 



When a parasite group is taxonomically well under- 

 stood, it can be treated as a host character with as 

 much validity as host morphology, serology, and 

 ecology. 



Objections or reservations regarding the parasite 

 approach to host phylogeny raised by Mayr (1957) 

 and Hennig (1966) are based on studies or examples, 

 using a relatively small number of parasite species, 

 usually within one parasite taxon (genus or family). If, 

 however, one repeats the analysis of the same hosts 



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