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Fishery Bulletin 97(2), 1999 



larger than this size could also be infested by con- 

 suming infected second-intermediate hosts, such as 

 copepods and other crustaceans. 



Infestation in the smaller rhynchoteuthions may 

 occur when free cystophorous cercariae are released 

 into the plankton and passively enter the mantle cav- 

 ity during respiration ( Gaevskaya, 1976 ) or when the 

 cercariae attach to mucus that covers the mantle and 

 head of rhynchoteuthions. They may also be ingested 

 directly, in the same way that crustaceans are in- 

 fested. If this is true, ommastrephid paralarvae may 

 act as second intermediate hosts for some didy- 

 mozoids. The presence of didymozoid metacercariae 

 in the digestive tracts of rhynchoteuthions as small 

 as 2.0 mm ML shows that the infection occurs well 

 before that previously recorded by Gaevskaya and 

 NigmatuUin (1983). Additionally, the size of the 

 didymozoid metacercariae type Monilicaecum (140- 

 200 |.im) found on rhynchoteuthion paralarvae is 

 strong evidence that they are in an early develop- 

 mental stage in relation to those found on adult /. 

 argentinus from southern Brazil (400-800 |.im) 

 (Santos, 1992). Our results are in accordance with 

 the suggestion of Hochberg ( 1990) that didymozoids 

 can grow inside the squid host. Hochberg ( 1990 ) also 

 reported that a peak of infestation by didymozoids 

 occurs in squids from 10 to 25 cm in ML. Nevertheless, 

 infection decreases in adult individuals ( Gaevskaya and 

 NigmatuUin, 1977. 1983) owing to the fact that the 

 didymozoids die after they reach a maximum size in a 

 specific host (Hochberg, 1990). Larger squids may 

 be reinfected by didymozoid metacercariae when they 

 feed on infested fish prey (Hochberg, 1990). Our re- 

 sults indicate that more paralarvae should be exam- 

 ined in the future. If it is correct to assume that re- 

 cently hatched didymozoid metacercariae usually 

 infest early paralarvae, information on size and de- 

 velopmental stage of both host and parasites would 

 help to understand their relationship better. 



Didymozoid metacercariae were found in /. argen- 

 tinus rhynchoteuthions from autumn to spring and 

 in "type A" rhynchoteuthions during the summer. 

 This morphotype had a higher prevalence and infes- 

 tation of didymozoids than those of/, argentinus. 

 They were collected in the summer of 1990, when 

 tropical waters dominate the study area (Vidal and 

 Haimovici, 1997). Thus, these larval trematodes are 

 present off southern Brazil throughout the year This 

 finding is in agreement with the occurrence of the 

 high prevalence and intensities of didymozoid meta- 

 cercariae in juvenile and immature /. argentinus from 

 the same area year around (Santos, 1992). 



Only the sexual stages ofAggregata occur in cepha- 

 lopods, whereas asexual stages infect the digestive 

 tracts of crustaceans (Hochberg, 1990). Aggregata 



appears to be host-specific only in cephalopods, not 

 in crustaceans, and is a common parasite of Sepia 

 and Octopus (Hochberg, 1990). Our study is the first 

 to report its presence in /. argentinus. This coccidian 

 has not been found in adults of/, argentinus collected 

 off southern Brazil (Santos, 1992) or Argentina 

 (NigmatuUin and Shukhgalter, 1990; Sardella et al., 

 1990 ). Martial ia hyadesi, a southern Atlantic oceanic 

 species, and Todaropsis eblanae and Todarodes sagit- 

 tatus in waters off Spain are the other ommastrephid 

 squids in which Aggregata have been reported 

 (Gaevskaya et al. 1986, Pascual et al. 1996). It is 

 important to stress that infections hy Aggregata can 

 only be established after paralarvae begin to feed on 

 crustaceans infected with the asexual stages of the 

 parasite. The infected paralarva observed in this 

 study was 7.8 mm ML; however, crustacean prey, 

 mainly copepods, have been found in the gut of /. 

 argentinus paralai-vae larger than 3.7 mm ML (Vidal 

 and Haimovici, 1998). 



Metacaligus uruguayensis was originally described 

 from the gill cavity of Trichiurus lepturus from Ven- 

 ezuela (Ho and Bashirullah, 19771. This genus pre- 

 viously has not been reported from cephalopods (see 

 review by Hochberg, 1990). Associations between 

 copepods and cephalopods appear to be primarily 

 commensal and not truly parasitic (Hochberg, 1990). 

 In southern Brazil, small and large adult T. lepturus 

 (70-1000 mm TL) occasionally prey on juvenile and 

 adult/, argentinus (22-200 mm ML) (Martins, 1992); 

 however, additional information is required to de- 

 termine whether /. argentinus serves as a final or 

 only an accidental host for this copepod. 



Acknowledgments 



We would like to thank F. G. Hochberg for his valu- 

 able review of the manuscript and for examining the 

 coccidian parasites. We also thank G. A. Boxshall for 

 his support and for the identification of the copepod 

 parasite. E. A. G. Vidal was supported by the Brazil- 

 ian National Research Council (CNPq). 



Literature cited 



Castellanos, Z. J. A. 



1960. Un:i nueva especie de calamar Argentino Omnia- 

 strcphcs argentinus sp. nov. (Mollusca. Cephalopoda). 

 Nt'olropica 6( 20):.5.5-58. 

 (laevskaya, A.V. 



1976. On tht> hflminthofauna of the Atlantic squid Omma- 

 stifplii's bartramii Le.sueur. In Biological fisheries re- 

 search in Atlantic Ocean. AtanNIRO Works 69:89-96. |In 

 Russian.] 



