FISHERY BULLETIN: VOL. 81, NO. 2 



index to host specificity at the generic level than that 

 based solely on literature. The Silas and Ummer- 

 kutty data indicate a higher specificity at the level of 

 1 genus of host; they also indicate a higher percent- 

 age of "generalists" (36% with 3 or more genera plus 

 nonscombrids). Furthermore, the Cressey and Cres- 

 sey and later data indicate a gradual transition from 

 greater to lesser host specificity, whereas the data 

 based on Silas and Ummerkutty do not. 



Comparison of percent specificity (percent species 

 with only one host, see Price 1980:123) shows a wide 

 range of specificity per genus of scombrid copepod 

 parasites (Table 5). Specificity to a genus of hosts 

 seems more meaningful to us, so we have also cal- 

 culated these figures. Six of the seven families that 

 contain scombrid copepod parasites show relatively 

 high percent specificity at the generic level (50-75%) 

 while the Caligidae is distinctly lower (35%). 



Scombrinae 



The subfamily Scombrinae is composed of two 

 groups of two tribes. The more primitive mackerels 

 (Scombrini) and Spanish mackerels (Scomberomo- 

 rini) have a distinct notch in the hypural plate, lack 

 any bony support for the median fleshy caudal pe- 

 duncle keels, and do not have the penultimate verte- 

 bral centra greatly shortened. 



Scombrini 



The tribe Scombrini contains the two genera of 

 mackerels, Scomber and Rastrelliger. Mackerels have 

 small conical teeth and a large number of gill rakers. 

 Characters differentiating the two genera have been 

 given by Matsui (1967:table 4). 



Copepod fauna: 9 species in 7 genera. Bomolochid 

 copepods can be separated into two subgroups based 

 on the presence of one or two major setae (in addition 

 to the remainder of the normal complement) on each 

 caudal ramus. The genera found on Scomber and R. 

 brachysoma (Pumilopes, Orbitacolax, and Nothobo- 

 molochus) are members of the group with one major 

 terminal seta. Although members of this same cope- 

 pod subgroup are found on other fish families, none 

 are found on other scombrids. This host specificity of 

 some members of that subgroup to the Scombrini 

 distinguishes the true mackerels from the other scom- 

 brid tribes. Pumiliopes jonesi is the only copepod 

 found in both genera of Scombrini and nowhere else, 

 occurring in the orbits of two species of each genus. 

 The infestation rate in Rastrelliger was 13%, in Scom- 

 ber only 2%. 



TABLE 5.— Percent specificity (percent species with only one 

 host) and percent generic specificity (percent species with 

 hosts only in one genus) in genera of copepod parasites of 

 scombrid fishes. 



Scomber Linnaeus 



We follow most recent authors (Fraser-Brunner 

 1950; Collette and Gibbs 1963; Matsui 1967) in con- 

 sidering Pneumatophorus a synonym of Scomber. 

 Scomber differs from Rastrelliger in a number of ana- 

 tomical characters which have been summarized by 

 Matsui (1967:table 4). Copepod fauna: 5 species in 4 

 genera. Only the lerneopodid Clavellisa scombri is 

 restricted to Scomber, occurring on gills of Scomber 

 japonicus and S. australasicus in our material. It was 

 originally described from a host identified as S. scom- 

 brus from Trieste, but we failed to find it in 97 speci- 

 mens of that species. 



Matsui (1967) recognized three species oiScomber. 

 S. scombrus Linnaeus in the North Atlantic and Med- 

 iterranean; S. australasicus Cuvier in the western 

 Pacific from Japan to southern Australia east to the 

 Hawaiian Islands, and across the eastern Pacific bar- 

 rier to Socorro Island off Mexico; and S. japonicus 

 Houttuyn, a worldwide antitropical species. All the 

 copepod species known from the three species have 

 been found on S. japonicus, of which we have examin- 

 ed about 500 specimens. 



Rastrelliger Jordan and Starks 



Matsui (1967:table 4) summarized the diagnostic 

 characters of Rastrelliger. Copepod fauna: 5 species 

 in 5 genera. Pumiliopes jonesi and two other bomo- 



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