BRILL ET AL.: INFECTION OF DORSAL AORTA IN YELLOWFIN TUNA 



the Gulf of Mexico, found no apparent detrimen- 

 tal effect on the host, but these parasites were 

 found encysted in the muscle, not the vascula- 

 ture. Although the ability of parasitized yellowfin 

 tuna to function as predators are apparently not 

 affected, their ability to escape predation remains 

 to be tested. It is possible that infected yellowfin 

 tuna are subjected to differential predation, as 

 has been shown to be for roach, Rutilus rutilus, 

 infected in the coelomic cavity by the plerocercoid 

 of Ligula sp. (Van Dobben 1952). 



Pressure Flow Relationships in 

 the Dorsal Aorta 



The unphysiologically high pressures required 

 to pump saline through the dorsal aortas of mod- 

 erately and heavily infected fish remain to be ex- 

 plained in light of apparent lack of effects of the 

 parasite on other measures of the fish's condition, 

 including the absence of cardiac hypertrophy. It is 

 possible that the dorsal aorta, because of its thick 

 muscular wall (J. Brock, unpubl. obs.), becomes 

 significantly less compliant postmortem. Such 

 changes could require that higher pressures be 

 generated to create a given degree of expansion. 

 Therefore higher pressures would be required 

 postmortum to push a given flow rate of saline 

 through the vessel. 



In summary, D. talismani appears to have no 

 significant adverse effects on the physiological 

 fitness and natural mortality of small yellowfin 

 tuna in spite of apparent vascular blockage. How 

 these fish are able to cope with dorsal aorta infec- 

 tion requires further investigation. 



Use of Dasyrhynchus talismani as 



a Natural Tag for Tracing 

 Movements of Small Yellowfin Tuna 



We feel that this parasite offers excellent po- 

 tential as a natural marker for tracking the 

 movements of separate groups of small yellowfin 

 tuna between or into specific fisheries. (For a re- 

 view of the use of parasites to delineate stocks for 

 management purposes, see MacKenzie 1983.) 

 Dasyrhynchus talismani does not fulfill all seven 

 requirements for an ideal natural tag listed by 

 Sindermann (1983), but it does appear to meet the 

 requirements of 1) having significant differences 

 of geographic prevalence, 2) being easily detected, 

 3) being able to be definitively identified, 4) hav- 

 ing minimum effect on host survival, and 5) sur- 

 viving in the host for long periods. Data on preva- 



lence ofD. talismani could be combined with data 

 on prevalence of other parasites, as has been 

 shown by Lester et al. (1985) for skipjack tuna, or 

 combined with data on relative condition factor, 

 relative heart weight, and relative liver weight to 

 provide information on fish movements. 



ACKNOWLEDGMENTS 



The authors wish to express their appreciation 

 to David Jones (University of British Columbia) 

 for drawing our attention to this problem, and to 

 Frank Goto and Brooks Takanaka of the United 

 Fishing Agency (Honolulu, HI) for allowing us to 

 inspect and take samples fi-om yellowfin tuna on 

 the auction floor. We also thank Greg Webber for 

 his data-collecting work, Theresa Villanueva for 

 reviewing the literature, Dave Karl and Chris 

 Winn (University of Hawaii) for helping with the 

 RNA/DNA analyses, Michael Hadfield (Univer- 

 sity of Hawaii) for allowing us to use his Cahn 

 microbalance, and Carol Hopper (Waikiki Aquar- 

 ium) and Terry Foreman (Inter- American Tropi- 

 cal Tuna Commission) for reviewing drafts of this 

 manuscript. 



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