RESPIRATION RATES AND LOW-OXYGEN TOLERANCE LIMITS IN 

 SKIPJACK TUNA, KATSUWONUS PELAMIS 



Reginald M. Gooding/ William H. Neill,'^ and Andrew E. Dizon^ 



ABSTRACT 



Oxygen-uptake rates and swimming speeds of voluntarily active skipjack tuna, Katsuwonus pelamis, 

 at 23°-24° C were measured in the laboratory from captivity-habituated fish (0.6-3.8 kg) and at sea 

 from just-caught fish (L8-2.2 kg). In the shipboard tests, skipjack tuna swam 2-5 lengths/s (length = 

 fork length) and consumed 0.9-2.5 (median = 1.3) mg Oa/g per h during their first 2.2 h of captivity. 

 In laboratory tests, skipjack tuna swam at a mean speed of L4 lengths/s and consumed oxygen at a 

 mean rate of 0.52 mg Oa/g per h. For the laboratory fish, routine swimming speed (S, in lengths/ 

 second) was inversely related to fish weight ( W, in grams) — S = 3.12 - 0.53 logio W; oxygen-uptake 

 rate ( Vq^ , in milligrams Oz/gram per hour) was directly related to both weight and speed (i.e., speed 

 independent of weight effects) — logioVOj = -1-20 + 0.19/logioW + 0.21 S. However, laboratory fish 

 swimming at their characteristic (weight dependent) speeds respired at rates independent of weight. 

 Calculations based on the above interrelations among metabolic rate, swimming speed, and body 

 weight indicated that skipjack tuna of all sizes may have an optimum swimming speed (for maximum 

 distance per unit energy expenditure) near 2.1 lengths/s. 



Captivity-habituated skipjack tuna (0.8-3.4 kg) also were subjected to a step decrease in concen- 

 tration of dissolved oxygen (O2) at 23°-24° C to determine their responses to acute hypoxia. At levels 

 of O2 below 4 mg/1, voluntary swimming speed increased as O2 declined, reaching 3.9 lengths/s at the 

 lowest test value of O2 , 1.4 mg/1. The 4-h median tolerance limit for low O2 proved similar to the O2 

 level critical for change in swimming speed, about 4 mg/1. 



Experimental results are analyzed and compared with those from other fishes to arrive at the 

 following conclusions: 1) The skipjack tuna's "standard" metabolic rate is two to five times that of 

 typical fishes of similar size; 2) the weight exponent for "standard" metabolic rate of skipjack tuna is 

 a positive value near 0.2, as opposed to the -0.2 value tjrpical of fishes; 3) but, because the 

 characteristic swdmming speed of routinely active skipjack tuna is inversely related to weight, 

 routine metabolic rate is virtually independent of fish weight; 4) highly active skipjack tuna can 

 consume oxygen from air-saturated sea water at rates exceeding those known from any other fish of 

 similar size; and 5) the skipjack tuna is relatively inefficient in its use of oxygen and food-energy for 

 swdmming (at least at low speeds) and it dies at O2 levels still well above those lethal for other fishes. 



Until the mid-1960's the environmental require- 

 ments of commercially important tunas (Scom- 

 bridae) were known mainly from correlations 

 between fishery catch rates and oceanographic 

 conditions (see discussions by Robins 1952; Laev- 

 astu and Rosa 1963; Broadhead and Barrett 1964; 

 Blackburn 1965; Williams 1970; Blackburn and 

 Williams 1975; Matsumoto 1975). With the ad- 

 vent of techniques for studying tunas in captivity 

 (Magnuson 1965; Nakamura 1972), many unre- 

 solved issues of tuna biology could be explored 

 such as feeding and gut-evacuation rates (Mag- 

 nuson 1969), auditory perception (Iversen 1967), 

 visual perception (Nakamura 1968; Tamura et al. 



'Southwest Fisheries Center Honolulu Laboratory, National 

 Marine Fisheries Service, NOAA, 2570 Dole St., Honolulu, 

 HI 96812. 



^Department of Wildlife and Fisheries Sciences, Texas A&M 

 University, College Station, TX 77843. 



Manuscript accepted September 1980. 

 FISHERY BULLETIN: VOL. 79, NO. 1, 1981. 



1972), thermoperception (Dizon et al. 1974, 1976; 

 Steffel et al. 1976), nerve-muscle physiology 

 (Rayner and Keenan 1967), tissue metabolism 

 (Gordon 1968), respiratory physiology (Stevens 

 1972), body temperature and thermal inertia 

 (Stevens and Fry 1971; Neill et al. 1976), lethal 

 temperatures (Dizon et al. 1977), swimming me- 

 chanics (Magnuson 1970), and swimming speed 

 as a function of water temperature (Stevens and 

 Fry 1971; Dizon et al. 1977), dissolved oxygen (O2 ) 

 concentration, and salinity (Dizon 1977). In addi- 

 tion, several works of a more integrative nature 

 (Magnuson 1973; Barkley et al. 1978; Kitchell et 

 al. 1978; Stevens and Neill 1978) have drawn 

 heavily on these and unpublished laboratory 

 studies. Among the latter are the experiments 

 documented in this paper on oxygen-uptake rates 

 and limits of tolerance to low oxygen in skipjack 

 tuna, Katsuwonus pelamis. 



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