FISHERY BULLETIN: VOL. 85, NO. 4 



ports involve the single parasite species, D. talis- 

 mani, this parasite is both common and ubiqui- 

 tous. 



Because of the apparent vessel blockage by par- 

 asites and tissue inflammation, we hj^jothesized 

 that infected fish would be severely activity lim- 

 ited and not function well as predators. If so, in- 

 fected fish should show evidence of short- and/or 

 long-term food deprivation, including lower rela- 

 tive condition factors, smaller livers, and slower 

 long- and short-term growth rates (Bulow 1970; 

 Pollard 1971, 1973; Bulow et al. 1981). We also 

 expected blockage of the dorsal aorta to cause in- 

 creased blood pressures, increased cardiac work, 

 and therefore cardiac hypertrophy (Poupa and 

 Ostadal 1969). 



To test our hypotheses, we measured fork 

 length, body weight, liver weight, and ventricle 

 weight from parasitized and unparasitized fish. 

 We also determined RNA/DNA ratios as a mea- 

 sure of the parasite's effects on short-term growth 

 rates (Bulow 1970; Bulow et al. 1981), and rela- 

 tive otolith weights as a measure of the parasite's 

 effects on long-term growth rates. Since otolith 

 weights are linearly related to a fish's chronolog- 

 ical age (Boehlert 1985), fish that are older at a 

 given body size should have relatively heavier 

 otoliths. We also recorded the prevalence of infec- 

 tion in small (<3 kg) and large 045 kg) yellowfin 

 tuna, and in skipjack tuna, Katsuwonus pelamis, 

 kawakawa, Euthynnus affinis, and bigeye tuna, 

 T. obesus. Additionally, monthly prevalence in 

 small yellowfin tuna was noted. 



To measure directly the effect of the occlusion 

 caused by the parasites and host inflammation, 

 we used an in vitro perfusion test. We measured 

 the pressure required to push various saline flow 

 rates down the dorsal aorta in freshly dead in- 

 fected and uninfected fish. 



MATERIALS AND METHODS 



Sampling Procedures 



The small tunas (0.2-3 kg body weight) used in 

 this study were captured at sea near Oahu, HI, 

 returned alive to be held in shoreside tanks at the 

 Kewalo Research Facility (National Marine Fish- 

 eries Service, Southwest Fisheries Center Hon- 

 olulu Laboratory), or sacrificed at sea and held on 

 ice. During necropsy, fork length and body weight 

 were measured, ventricles and livers were re- 

 moved, blotted dry, and weighed to the nearest 10 

 mg. Only those fish in captivity for 3 days or less 



were included in the data for condition factor, and 

 relative heart and liver weights. Large yellowfin 

 tuna (>45 kg body weight) were examined at the 

 Honolulu Fish Auction for the presence of dorsal 

 aorta parasites while the fish were being pre- 

 pared for sale. All fish were examined within 24 

 hours of death. 



Thirty-five live yellowfin tuna, from one school, 

 were caught 15 January 1986 and transported 

 alive to the Kewalo Research Facility. Im- 

 mediately upon arrival, the animals were sacri- 

 ficed, weighed, and measured. Lateral white 

 muscle samples were taken within 4 minutes of 

 death and immediately frozen on dry ice. These 

 samples were subsequently used for measure- 

 ment of RNA/DNA ratios using the Schmidt- 

 Thannhauser procedure as described in Murno 

 and Fleck (1966). The ventricles and livers of the 

 fish were also removed, blotted dry, and weighed 

 to the nearest 10 mg. Sagittal otoliths were re- 

 moved, cleaned, dried, and weighed to the nearest 

 microgram. 



Parasites for species identification were ob- 

 tained most often from the major artery within 

 the spleen of large (>45 kg) yellowfin tuna. After 

 being removed from a surrounding capsule, para- 

 sites were placed in tap water until the holdfasts 

 everted. 



For histological examination, sections of dorsal 

 aorta were fixed in 10% buffered formalin and 

 processed by routine laboratory procedures. Tis- 

 sue sections were stained with hematoxylin and 

 eosin. 



Direct Measurement of 



Pressure-Flow Relationships in 



the Anterior Dorsal Aorta 



To quantify blockage, we choose to measure the 

 pressures required to push various flow rates of 

 saline through the anterior dorsal aorta of in- 

 fected and uninfected fish. The dorsal aorta of 

 freshly killed fish was exposed from the conflu- 

 ence of the efferent arteries of the first and second 

 gill arches to the point where it enters the first 

 hemal arch. All efferent and afferent vessels were 

 tied off except for the confluence of the efferent 

 arteries from either the left or right first and sec- 

 ond gill arches. This portion of the vessel was cut 

 and a short length of flared polyethylene tubing 

 (PE160, 2.4 mm OD) inserted. The dorsal aorta 

 was also transected at the point where it entered 

 the first hemal arch to allow the saline perfusate 

 to flow out. Parasites were never found poste- 



768 



