Macy et a!,; Metabolic rate of Brevoortia tyrannus 



289 



1.000 



0.100 



0.010 



10°C 



R = 0.040 X e '^ ^^■^ " ^\ r-^ = 0.994 



10 20 30 40 50 60 70 



— 1.000 



00 



M 0.100 



E 



o. 



D 



d* 



0.010 



15°C 



R = 0.073 xe'°°22''S)^ ^2^0 



898 



I I I I , I I I I I I I I I ,, I 



10 20 30 40 50 60 70 



1.000 r 



20°C 



0.100 



R = 0087 xe '0020x5)^^2^0 



963 



-+n 



-1^ 



-1^ 



r4^ 



r-l- 



-A 



0.010 



10 20 30 40 50 60 70 



Mean SS, cm/s 



Figure 5 



Relation between metabolic rate and swimming speed 

 offish in the respirometer at 10", 15", and 20°C. 



to routine rates calculated from Hettler's data (Table 

 3) that indicate that a 300-g menhaden at 10"'C would 

 have a routine metabolic rate of 0.073 mg 0.,/(g wet 

 wt • h) and to previously cited observations by Durbin 

 et al. ( 1981) on routine swimming and metabolic rates 

 in menhaden at 20°C. Johnstone et al. (1993) re- 

 ported routine metabolic rates of 0.118 mgOV(gwet 

 wt • h) for 290-380 mm Atlantic mackerel. Scomber 

 scombriis, swimming at 0.6 BL/s at 11.1°C, and 0.093 

 mg 0,/(g wet wt • h) for 255-310 mm Atlantic her- 

 ring, Cliipea harengus, swimming at 0.3 BL/s at 

 9.3°C. Because these routine swimming speeds were 

 lower than previously reported by these investiga- 

 tors (0.9-1.2 BL/s for mackerel, and 2 BL/s for her- 

 ring) and because the fish were maintained for a pro- 

 longed period in the respirometer without feeding 



(5-16 d for mackerel, 13 d for herring), these may be 

 under-estimates. Routine activity and metabolic 

 rates in menhaden thus may be lower than in her- 

 ring and mackerel. 



Durbin et al. ( 1981 ) noted that the actual measured 

 routine metabolic rate in menhaden was higher than 

 that predicted for the same swimming speed by us- 

 ing the swimming-speed and metabolic-rate relation- 

 ship during feeding. This higher routine rate was as- 

 sumed to reflect increased excitability in fish when 

 not occupied by feeding and also the more variable 

 and energetically less efficient mode of swimming 

 associated with routine activity. Routine swimming 

 also appears to be energetically more expensive than 

 forced swimming (as shown in our study) and directed 

 swimming, where the optomotor response is used to 

 induce fish to swim at a steady, but possibly more 

 variable, speed than in forced swimming. In a re- 

 view of ten species, three marine and seven fresh- 

 water, Boisclair and Tang ( 1993) found that routine 

 swimming was energetically the most expensive and, 

 on average, was 9.4 times higher (range: 6.4 to 14.0) 

 than forced swimming at the same speed. Directed 

 swimming ranged from 1.0 to 2.8 times as expen- 

 sive. Applying a similar analysis to menhaden at 



