ON THE STANDARD METABOLIC RATES OF TROPICAL TUNAS, ma INCLUDING THE EFFECT OF BODY SIZE AND ACUTE TEMPERATURE CHANGE

The standard metabolic rates (SMRs) of fishes and the effect of body weight on SMRs are important input parameters to energetiw, growth, and population models. This study was undertaken to ob \n &niS. These data compliment similar SMR measurements from skipjack tuna, Kahwonus pslamis, previously published. The effect of acute temperature change on the SMR of all three s p i e s waa also determined. The SMR was estimated by directly measuring the oxygen uptake rate of animals paralyzed with a neuromuscular blocking drug, rather than hy the more commonly used method of extrapolation of swimming speedmetabolic rate curves back to zero swimming speed. To test the adequacy of this technique, the SMR's of aholehole, KuMia sandvieensis, and rainbow trout, Salmo gairdnerii. were determined using similar methodology. The S M R s measured in this way were not significantly different from the published SMR's of these s p i e s determined by extrapolation of swimming speedmetabolic rate cumm back to zero swimming speed. All three tuna species have very high SMRs. over five times higher than other active teleost species such as aalmon and trout. The effect of body size on the SMR is similar in all three tuna species, but the weight specific SMR of tuna decreases more rapidly with increasing body size than in other fishes. Based on SMR's measured at 20" and 25T, the Q,;s were 3.16, 2.31, and 2.44 for yellowfin tuna, kawakawa, and skipjack tuna, respectively. These are similar to Q,o values found for the SMR's of other teleosts. Tunas can achieve exceptionally high maximum aerobic metabolic rates. This ability requires a complete set of anatomical. physiological, and biochemical adaptations. I hypothesize that one of these adaptations, large gill surface areas, causes tunas to have exceptionally high energy demands even at rest. Tunas' high SMR's are an inevitable consequence of their ability to achieve exceptionally high maximum aerobic metabolic rates. these data for the tropical tuna species, yellowfin tuna, Thunnw albaoares, and kawakawa, Euthyn %' w The standard metabolic rate (SMR) (the metabolic rate of a postabsorptive animal completely at rest) and the effect of body size on SMR are important input parameters to growth, energetics, and population models (e.g., Sharp and Francis 1976; Kitchell e t al. 1978). This study was therefore undertaken to obtain these data for yellowfin tuna, Thunnus albaeares, and kawakawa, Euthynnus afinis. These measurements were designed to directly compliment the SMR measurements for skipjack tuna, Katsuwonus pelamis, that had been previously published (Brill 1979). The effect of acute temperature change on the SMR of skipjack tuna, yellowfin tuna, and kawakawa was also determined. The effect of acute temperature change, as opposed to the effect of temperature adaptation, is relevant to tuna because of the 5 ' to 15°C water temperature changes 'Southwest Fisheries Center Honolulu Laboratory, National Marine FisheriesService, NOAA, 2670 Dole Street, Honolulu, HI 96822-2396. Manuscri t accepted November 1988. FISHER% BULLETIN: VOL. 85. NO. 1. 1987. these species normally experience during the daily vertical movements which are a constant feature of their behavior in the open Ocean (Dizon et al. 1978; Carey and Olson 1982; Yonemori 1982). In other teleosts, SMR's have been determined by extrapolating metabolic rate-swimming speed curves back to zero swimming speed (e.g., Brett 1965). Although Graham and Laurs (1982) have successfully measured the metabolic rate of albacore, T. alalungu, (a temperate tuna species) swimming in a water tunnel, this methodology is presently not possible with tropical tunas (skipjack tuna, yellowfin tuna, and kawakawa). Attempts to get these species to swim in several prototype water tunnel designs have shown that they will do so for only very short periods (Brill and Dizon 1979 and unpublished observations). As a result, measuring the S M R s of tropical tunas directly in animals paralyzed with a neuromuscular blocking agent is currently the only method available to obtain these data. To validate this technique, the SMR's of rainbow