plex are ubiquitous endoparasites of adult fishes 

 ( Appey and Burt 1982) including B rev o or tia tyrannus 

 (Meyers 1978). They also have been reported in the 

 alimentary canal of Clupea harengus larvae (Rosen- 

 thal 1967). Plerocercoids of the Scolex polymorphus 

 complex, a systematic composite that is similar to 8. 

 pleuronectis, infect a variety of fishes and inverte- 

 brates in the northern Gulf of Mexico (Overstreet 

 1978). Digenean hemiurid trematodes, but none of 

 the genus Aphanurus (Lebour 1918; MacKenzie 

 1974; Yamashita 1979), have been reported in larval 

 fishes of disparate taxa. Aphanurus sp. also infects 

 adult B. tyrannus (Meyers 1978). 



Prevalence of Infections 



The cooccurrence of cestodes and trematodes in 

 larval gulf menhaden did not indicate affinity. Scolex 

 pleuronectis and Aphanurus sp. cooccurred in only 2 

 of 64 (3. 1 % ) infected gulf menhaden larvae and never 

 in the 1 spot or the 4 Atlantic croaker larvae; the 

 theoretically expected coincidence of infection was 

 159c . The index of affinity was —0.02 where an index 

 >50 is expected if species show positive affinity 

 (Fager and McGowan 1963). Whereas Ogilvie (1927) 

 reported that most ('. harengus larvae in the North 

 Sea were infected simultaneously with both a ces- 

 tode and a trematode, Hentschel (1950) reported 

 only cestode infections of C. harengus in the North 

 and Baltic Seas. The present lack of affinity suggests 

 that S. pleuronectis and Aphanurus sp. do 

 not share a common intermediate host. 



The prevalence of infections (Table 1) differed 

 significantly among the three species of fishes 

 (Tables 2, 3). Scolex pleuronectis infected 26 of 1,067 

 (2.4%) gulf menhaden and 2 of 235 (0.8%) Atlantic 

 croaker larvae examined. No S. pleuronectis were 

 found in spot larvae. Aphanurus sp. infected 38 

 (3.6%) gulf menhaden, 1 (0.5%) spot, and 2 (0.8%) 

 Atlantic croaker larvae. The high prevalence of infec- 

 tion by both the cestode and the trematode in gulf 

 menhaden larvae and the corresponding low or com- 

 plete lack of infection by the cestode in spot and 

 Atlantic croaker larvae imply that diets differ. The 

 diets of these three species did differ significantly 

 with the diet of gulf menhaden larvae the most dis- 

 tinct (Govonietal. 1983). Gulf menhaden larvae ate a 

 more diverse diet that included phytoplankters 

 (mainly dinoflagellates) as well as zooplankters 

 (including tintinnids, pelecypods, pteropods, and all 

 stages of copepods). The diets of larval spot and 

 Atlantic croaker were restricted to zooplankton. 

 Significant differences in diet notwithstanding, the 

 lack of adequate systematic definition (the S. 

 pleuronectis complex), and the lack of tetraphyllidean 

 and hemiurid host specificity confound relationships 

 between helminth infections and diet among these 

 larval fishes. 



The prevalence of infections (Table 1) was lower 

 than previously reported helminth infections of lar- 

 val fishes caught at sea (Lebour 1918; Hentschel 

 1950; MacKenzie 1974). Previous reports have dealt 

 with larger fish larvae that were exposed to helminth 

 infection for longer periods (MacKenzie 1974) and 



Table 1.— The prevalence of cestode (Scolex pleuronectis) and trematode (Aphanurus sp.). infection in larval cohorts of 

 Brevoortio patronus. Leiostomus xanthuru.% and Micropogomas undulatus in the northern Gulf of Mexico. 



896 



