Table 2. — Tests of independence in the prevalence of cestode 

 (Scolex pleuronectis) infection among larval Brevoortia patronus, 

 Leiostomus xanthurus, and Micropogonias undulatus collected in 

 December 1979, February 1980, December 1980, and February 

 1981 in the northern Gulf of Mexico. 



TABLE 3— Tests of independence in the prevalence of trematode 

 (Aphanurus sp.) infection among larval Brevoortia patronus, Leio- 

 stomus xanthurus, andMicropogonias undulatus collected in Decem- 

 ber 1979, February 1980, December 1980, andFebruary 1981 in the 

 northern Gulf of Mexico. 



that ate greater numbers of copepods (Hentschel 

 1950). Copepods are the intermediate hosts of tet- 

 raphyllidean cestodes (Cheng 1950) and digenean 

 hemiurid trematodes (Gibson and Bray 1979). 



Although the prevalence of infections was low for all 

 species, it became greater in gulf menhaden and 

 Atlantic croaker larvae as length increased. No 

 helminths were found in larval gulf menhaden or 

 Atlantic croaker shorter than 5.01 mm. Scolex 

 pleuronectis infected only 2 of 557 (0.49c) gulf 

 menhaden larvae < 15.01 mm long but 24 of 386 

 (6.27c) larvae between 15.01 and 20.00 mm; 

 Aphanurus sp. infected no gulf menhaden larvae 

 < 15.01 mm, but 37 of 386 (9.6%) larvae between 

 15.01 and 20.00 mm. 



The prevalence of S. pleuronectis and Aphanurus 

 sp. infections (Table 1), being significantly (Tables 2, 



3) greater in February than in December, particularly 

 for gulf menhaden, may be related to differences in 

 the corresponding size of larvae and to ontogenetic 

 changes in their diets. Larger larvae, which had a 

 higher prevalence of infection, were more abundant 

 in February than in December. Spawning of gulf 

 menhaden during these years was bimodal with peaks 

 in late December and late January, 3 thus growth of 

 cohorts resulted in longer larvae in February collec- 

 tions. Inasmuch as gulf menhaden larvae did not eat 

 appreciable numbers of adult copepods until they 

 had grown longer than 5.01mm 2 , one would expect a 

 higher prevalence of helminth infection in months 

 when larger larvae were more abundant. Since the 

 length of the spot and Atlantic croaker larvae col- 

 lected changed little from December to February, a 

 seasonal trend in the prevalence of infection would 

 not be expected. 



Larval cohorts collected in the winter of 1979-80 

 (Table 1) showed a significantly greater prevalence 

 of infection than larvae collected in 1980-81 for both 

 S. pleuronectis (Table 2) and Aphanurus sp. (Table 

 3), but shifts in diet do not explain this difference. 

 Gulf menhaden larvae exemplified this annual dif- 

 ference in infection owing to the greater number of 

 larger larvae (>5.01 mm) collected and examined 

 from both winters. Larval gulf menhaden ate a 

 greater number and a greater diversity of copepods 

 in the winter of 1980-81 than in 1979-80 (Govoni et 

 al. 1983). 



Whether gulf menhaden, spot, and Atlantic croaker 

 larvae are definitive or paratenic (auxiliary) hosts for 

 members of the S. pleuronectis complex or Aphanurus 

 sp. are not known, due in part to the lack of sys- 

 tematic definition. In either case, the levels of infec- 

 tion in terms of the prevalence of infection as well as 

 the parasite loads on individual larvae are lower than 

 those that directly cause death of larval seabream 

 (Pagulus = Chrysophrys major) in the laboratory 

 (Yamashita 1979). Indirect effects of helminth infec- 

 tions (May 1983) on larval fish cohorts are not yet 

 clear. 



Acknowledgments 



I express my thanks to Joseph S. Sypek (Virginia 

 Institute of Marine Science) who kindly prepared 

 and identified the parasites, and to Thomas A. Mun- 

 roe( Virginia Institute of Marine Science) and Donald 

 E. Hoss and David R. Colby (NOAA-NMFS) who 



»S. M. VVarlen, Southeast Fisheries Center Beaufort Laboratory, 

 National Marine Fisheries Service, NOAA, Beaufort, NC 28516, 

 pers. commun. March 1982. 



897 



