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



rior to this point. Saline perfusion pressures, at 

 various constant flow rates provided by an infu- 

 sion pump, were recorded via a Uonix"* pressure 

 transducer. 



Calculation of Relative Condition 

 Factor and Relative Organ Weights 



Use of relative condition factor, and relative 

 organ and otolith weights allow groups of fish 

 containing individuals of a range of body sizes to 

 be directly compared (Pollard 1972). Using data 

 from unparasitized fish, regressions of body 

 weight (g) on fork length (cm), liver weight (g) on 

 body weight (g), and heart weight (g) on body 

 weight, were fitted by a least squares technique 

 to the exponential equation: 



Y = a- Xf" 



using a log-log transformation of the data. Rela- 

 tive condition factor and relative organ weights 

 for individual fish were calculated using the re- 

 gression parameters (a, 6 ) with the equation: 



K = W/a- XK 



For relative condition factor, W = body weight 

 and X = fork length. For relative organ weights, 

 W = liver or heart weight, and X = body weight. 

 The relationship of otolith weight (mg) to body 

 weight was found best fit with the simple linear 

 regression: 



Y = a + ib  X). 



Relative otolith weights were therefore calcu- 

 lated using the equation: 



K = WKa + b- X) 



where W = otolith weight and X = body weight. 

 A relative condition factor <1 indicates that an 

 individual is lighter for its fork length than pre- 

 dicted based on data from unparasitized fish. Sim- 

 ilarly, a relative liver or heart weight <1 indi- 

 cates a smaller liver or heart for a given body size 

 than that found for unparasitized fish. A relative 

 otolith weight >1 means that an individual expe- 

 rienced a relatively slower long-term growth rate 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



(i.e., is relatively older for a given body size and 

 therefore has a larger otolith). 



RESULTS 



Identification of the Parasite 



Tapeworms (class: Cestoda, order: Try- 

 panorhyncha) can be identified to species based 

 on scolex morphology and tentacular hooks 

 (onchotaxy), mature segments are not required. 

 The larval cestodes recovered from the yellow- 

 fin tuna during this study showed proboscis 

 chainettes flanked by a single row of inter- 

 calary hooks, a characteristic that distinguishes 

 Dasyrhynchus talismani from its congeners. 



This parasite was originally described from five 

 mature worms removed from the spiral valve of 

 Galeus glaucus (= Prionace glauca, the blue 

 shark) off" Cape Verde, West Africa (Dollfus 

 1935). Dasyrhynchus talismani has also been re- 

 ported in the Pacific from Carcharinus longi- 

 manus (Heinz and Dailey 1974). All other reports 

 describe plerocercoids from the vascular systems 

 of teleost fishes (Bussieras and Aldrin 1965; 

 Baudin Laurencin 1971; Chen and Yang 1973). 



Prevalence of hifection by 



Host Species, 



Fish Size, and Season 



A total of 53 skipjack tuna, 27 kawakawa, 10 

 bigeye tuna, and 470 yellowfin tuna were exam- 

 ined for the presence of parasites. We found only 

 yellowfin tuna to be infected. 



Infection in yellowfin tuna varied with size 

 class. We found a significantly lower incidence of 

 dorsal aorta infection in large fish. Of 220 indi- 

 viduals weighing 0.21 to 2.7 kg, 48% were in- 

 fected, while of 250 fish weighing more than 45 

 kg, only 5.2% carried the parasite in their dorsal 

 aortas. Viscera of a small subsample (N = 8) of 

 the larger fish were examined and indicated that 

 in larger fish the parasite infects (in the order of 

 prevalence) the major arteries of the spleen, in- 

 testinal caeca, liver, mesenteries, and lateral 

 blood vessels. Fish in intermediate size classes 

 were not available for this study. Fish >3 kg do 

 not survive the trip from the fishing grounds to 

 the Kewalo Research Facility and are therefore 

 not normally captured by commercial fishermen 

 for return to the laboratory. Fish <45 kg are not 

 common at the Honolulu Fish Auction where they 

 could be examined during normal processing. The 



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