GRAHAM: HEAT EXCHANGE IN SCOMBRIDS 



cardinal vein (Kishinouye 1923; Godsil 1954; Carey 

 et al. 1971; Carey 1973; Graham 1973). 



Kishinouye (1923: 377; see discussion of 

 Neothunnus, a synonym of T. albacares) described 

 a special subspinal vascular plexus or "kurochiai" 

 in the yellowfin tuna, T. albacares (Bonnaterre), 

 and recent studies have indicated that this struc- 

 ture is a central heat exchanger (Carey et al. 1971; 

 Carey 1973). The kurochiai has not been fully 

 described, nor has the relationship between it and 

 T. albacares' well-developed lateral heat 

 exchangers been considered. Body temperatures 

 of fresh-caught and swimming yellowfin tuna are 

 known to be less than those of skipjack tunas and 

 some other tuna when measured under similar 

 conditions (Barrett and Hester 1964; Carey and 

 Teal 1969b; Stevens and Fry 1971; Carey 1973), but 

 where heat is distributed in the body (thermal 

 profiles) has not been determined for either T. 

 albacares or the skipjack tuna K. pelamis (Lin- 

 naeus). 



The purpose of this study is to investigate the 

 relationship between body temperature and the 

 types of heat exchanger in T. albacares. The pat- 

 terns observed for this species and K. pelamis are 

 compared with those of other warm-bodied fish. 

 Body temperatures and thermal profiles of fresh- 

 caught T. albacares and K. pelamis are reported, 

 and their central heat exchangers are described. 

 The general structure and circulation pattern of 

 these species' heat exchangers are compared with 

 those of the bluefin tuna T. thynnus, and other 

 skipjack tunas, Euthynnus, and are discussed in 

 terms of their relation to differences in body 

 temperature, morphology, swimming capability, 

 and the natural history of these species. Studies of 

 this type may enable us to understand why there 

 are different kinds of heat exchangers and how 

 these evolved. 



MATERIALS AND METHODS 



Eleven T. albacares (360 to 700 mm fork length; 

 weight, 1 to 5 kg) and four K. pelamis (500 to 600 

 mm, 3 to 4 kg) were caught by surface trolling in 

 the Gulf of Panama and brought on board within 

 30 to 90 s of being hooked. Red and white muscle 

 temperatures of these specimens were immedi- 

 ately taken with a fast-reading hypodermic therm- 

 istor probe (Yellow Springs Instrument No. 513)- 



^Reference to trade names does not imply endorsement by the Na- 

 tional Marine Fisheries Service, NOAA. 



that had been calibrated against a mercury ther- 

 mometer. Measurements were made deep (near 

 the vertebrae), midway from the vertebrae to the 

 skin, and subcutaneously at several positions 

 along the fishes' lateral midplane, from the oper- 

 culum to the tail, in order to determine the relative 

 contribution of the lateral and central heat 

 exchangers to heat distribution. All temperatures 

 were rounded to the nearest 0.5°C. Body 

 temperatures of shaded fish remained fairly con- 

 stant during the first 10 min after capture, and all 

 measurements were made within this time. 



A criticism that has been directed against the 

 measurement and interpretation of temperature 

 data from fresh-caught fish is that burst swim- 

 ming to catch a troll lure, or frenzied swimming, 

 together with struggling once hooked may 

 increase body temperatures above typical values. 

 This probably has some validity, but the effects of 

 struggling and handling seem generally overrat- 

 ed. With telemetry, Carey (1973) has shown that 

 free-swimming T. thynnus have body tempera- 

 tures very similar to captured fish. Also, Barrett 

 and Hester (1964) found that immediately cap- 

 tured yellowfin tuna and those that had been 

 tethered for a few minutes had similar tempera- 

 tures. 



Large frozen T. albacares (800 to 1,400 mm, 8 to 

 42 kg) were obtained from a commercial fishing 

 vessel, and a range of sizes was dissected to de- 

 termine red muscle distribution, the position, size, 

 and structure of the heat exchangers, and the 

 dimensions of retial vessels. Specimens of K. 

 pelamis were also dissected, and measurements 

 were made. 



RESULTS 



Body Temperatures 



Average deep, intermediate, and subcutaneous 

 red muscle temperatures of eight T. albacares 

 (caught in surface water of 28.5°C) were 30.5°, 

 30.5°, and 29.5°C. Three specimens caught in 30°C 

 water had average deep body temperatures of 

 32.5°C. Elevated temperatures in T. albacares oc- 

 cur along the body from the pectoral fins to as far 

 as the third or fourth finlet. The warm region also 

 extends laterally through a large portion of the red 

 muscle. Highest body temperatures were always 

 found in the red and white muscle along and near 

 the lateral midplane of the body. Katsuwonus 

 pelamis is warmer than T. albacares, and its warm 



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