FISHERY BULLETIN: VOL. 85, NO. 1 



trout, Salmo gairdneri, and aholehole, Kuhlia sand- 

 vicensis, were also measured using paralyzed ani- 

 mals. These two species were chosen because they 

 are available in Hawaii and because there are pub- 

 lished data on their SMR's based on extrapolation 

 of swimming speed-metabolic rate curves back to 

 zero swimming speed (Muir et al. 1965; Bushnell et 

 al. 1984). 



The SMR of a 1 kg skipjack tuna (412 mg Og/h, 

 Brill 1979), is almost five times greater than that 

 of a 1 kg sockeye salmon, Oncorhynchus nerka (83 

 mg 02/h, Brett and Glass 1973). The former mea- 

 surements were made at 25 °C and the latter at 

 20°C, because 25°C is the upper lethal temperature 

 for salmon (Brett 1972). However, a 5°C tempera- 

 ture difference could not account for this SMR dif- 

 ference because the Qio's for the SMR's of fishes 

 are generally about 2 (Robinson et al. 1983). The 

 maximum sustainable aerobic metabolic rate (MMR, 

 the metabolic rate at the maximum swimming speed 

 sustainable for at least 1 h) of a 1 kg sockeye salmon 

 at 20°C is 796 mg 02/(kg-h), whereas 1.8-2.2 kg 

 skipjack tuna at 24°C have been shown to be able 

 to achieve active metabolic rates over 2,000 mg 

 02/(kg-h) (Gooding et al. 1981). Although there are 

 no metabolic rate measurements available for tunas 

 at their maximum sustainable swimming speeds, 

 two conclusions are still obvious: 1) skipjack tuna 

 have very high SMR's even when compared with 

 other active equal sized teleosts and 2) skipjack tuna 

 are capable of very high aerobic metabolic rates. 



I hypothesize that the high SMR's of tunas are 

 primarily a result of their large gill surface areas 

 (Hughes 1979). In other words, adaptations that per- 

 mit high maximum sustainable rates of oxygen up- 

 take (i.e., high MMR's) obligate tunas to have high 

 SMR's. Analogous arguments with respect to the 

 resting and maximal metabolic rates of terrestrial 

 vertebrates have been presented by Bennett and 

 Ruben (1979). 



MATERIALS AND METHODS 



SMR Measurements-Tuna 



Live skipjack tuna, yellowfin tuna, and kawakawa 

 were purchased from local fishermen and main- 

 tained at the Kewalo Research Facility (Southwest 

 Fisheries Center Honolulu Laboratory, National 

 Marine Fisheries Service, NOAA). Animal procure- 

 ment, handling, and maintenance procedures at this 

 facility are described by Nakamura (1972), Queenth 

 and Brill,^ and Chang et al.^ Fishes were main- 

 tained in outdoor tanks for a few days to over 1 yr 



before use. Temperature of the seawater supplied 

 to the holding tanks was 25°C ( + 2). Food was pre- 

 sented daily; however, individuals were not fed for 

 at least 20 h prior to use in an experiment. This 

 allowed sufficient time for gut clearance and for 

 blood glucose level to return to prefeeding levels 

 (Magnuson 1969). 



Each experimental animal was removed from its 

 holding tank by dip net and injected intramuscular- 

 ly with 1-3 mg/kg of the neuromuscular blocking 

 agent Flaxedil"* (gallamine triethiodide). The animal 

 was quickly returned to its holding tank, and when 

 it could no longer swim, it was immediately rushed 

 into the laboratory and placed in a Plexiglas flow- 

 through box respirometer similar to that used by 

 Stevens (1972). The respirometer was equipped with 

 a movable partition which was placed immediately 

 behind the fish to reduce the respirometer' s volume 

 and, thus, reduce the lag time between actual and 

 measured changes in metabolic rate to only minutes 

 (Niimi 1978). Water flow through the respirometer 

 was maintained at 3-7 L/(kg- min) and was measured 

 every 30-60 min by recording the time to fill a 1 L 

 graduated cylinder. Water temperature was con- 

 trolled by a chiller and freshwater heat exchanger 

 and by a quartz heater mounted in the inflow sea- 

 water line. Temperature control was ±0.3°C. 



Unlike the previous study on the SMR of skipjack 

 tuna (Brill 1979), the spinal cord was not cut to stop 

 all overt muscular activity. Rather, an 18-gauge 

 hypodermic needle was placed intramuscularly and 

 connected to the outside of the respirometer via a 

 short length of polyethylene tubing. Through this 

 tube, 0.1-0.3 mL doses of Flaxedil were adminis- 

 tered when the fish began to show any slight tail 

 movements. To monitor heart rate, electrocardio- 

 gram leads were mounted subcutaneously on the 

 ventral body surface. Heart rate was determined by 

 timing the interval between successive beats with 

 a Hewlett-Packard (HP) 5308A frequency counter. 

 Thermistors were used to measure fish muscle and 

 water temperatures. With the aid of an 18-gauge 

 hypodermic needle, a thermistor bead mounted in 

 0.9 mm diameter polyethylene tubing was inserted 



2Queenth, M. K. K., and R. W. Brill. 1983. Operations and pro- 

 cedures manual for visiting scientists at the Kewalo Research 

 Facility. Southwest Fisheries Center Honolulu Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, Honolulu, HI 96822-2396, 

 Administrative Report H-83-7, 16 p. 



^Chang, R. K. C, R. W. Brill, and H. 0. Yoshida. 1983. The 

 Kewalo Research Facility, 1958 to 1983—25 years of progress. 

 Southwest Fisheries Center Honolulu Laboratory, National Mar- 

 ine Fisheries Service, NOAA, Honolulu, Hawaii 96822-2396, Ad- 

 ministrative Report H-83-14, 28 p. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



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