STUDIES OF TROPICAL TUNA SWIMMING PERFORMANCE IN A LARGE WATER TUNNEL.1. ENERGETICS

The metabolic rates (V-O2) of three tropical tunas [yellowfin tuna (Th unnus albacares), kawakawa (Euthynnus affinis) and skipjack (Katsuwonu s pelamis)] were estimated using a large water-tunnel respirometer. Ex periments lasting up to 31h were used to determine the effects of velo city (U) on tuna V-O2 over a range of U (17 - 150 cms(-1)) and tempera tures (18-30 degrees C). Replicate tests were carried out on several f ish. The swimming V-O2 of yellowfin is temperature-dependent (Q(10)=1. 67, determined over intervals of 3-5 degrees C). For yellowfin and ski pjack, it was also possible to partition metabolic costs between maint enance and locomotion. The standard metabolic rate (SVO2) was estimate d by extrapolation of the U/V-O2 function to U=0. Comparisons of SVO2 for different size groups of yellowfin show that the mass-specific sca ling exponent for V-O2 is -0.40. The SVO2 of tuna is comparable to val ues determined previously by stasis respirometry and is approximately three times higher than that of salmonids. Further comparisons with sa lmonids show that the slope of the U/V-O2 function is less for tunas, which demonstrate a greater swimming efficiency.