Ikeda Energy budget of Maurolicus muellen 



55 



0.3 /iLOj/lmgWW-h) at 16.5-22°C ( median 19°C) for 

 specimens weighing 25-189 g WW (median 48.5 g 

 WW). For mesopelagic fishes off southern California, 

 Torres et al. (1979) reported 0.059-0.095 ph 2 /(mg 

 WWh) (mean 0.073 pL OgAmg WWh)) at 10°C on 

 four species weighing 2.1-9.3 g WW ( mean 6. 1 g WW ). 

 Because body size and temperature are two domi- 

 nant factors affecting oxygen consumption, direct 

 comparison with the present data on M. muelleri is 

 not possible. To overcome this problem, the specific 

 oxygen consumption data given by these previous 

 workers were extrapolated to the mean size of M. 

 muelleri (429 mg WW) used for ETS assay, assum- 

 ing size-dependent metabolism as mentioned above 

 (R«WW 085 ), and adjusted to the rates at 12°C by us- 

 ing a factor for temperature adjustment in Winberg 

 ( 1956). As a result, we obtain 0.31 /jL CX/dng WWh) 

 for the Pacific sardine, and 0.11 pL O.^mg WWh) 

 for four mesopelagic fishes off southern California. 

 Specific oxygen consumption rates for M. muelleri 

 (0.225 pL O/mg WWh)) estimated from ETS activ- 

 ity in this study fall near the center of the range of 

 these high epipelagic and low mesopelagic rates. 

 Lower specific oxygen consumption rates of deeper 

 living fishes are attributed to their greatly reduced 

 locomotion (Torres et al., 1979). From this view, the 

 results of this comparison suggest differential activ- 

 ity levels for each fish. The activity of M. muelleri is 

 relatively lower than that of the Pacific sardine but 

 higher than those of its mesopelagic counterparts off 

 southern California. 



The Q 10 = 3.52 derived from the relationship be- 

 tween the ETS activity and temperature for M. 

 muelleri (Fig. 2) in the present study appears rather 

 anomalous (i.e. Q 10 =2 to 3 for various biological pro- 

 cesses, cf. Prosser, 1961) but is close to Q 10 = 3.90 

 and 3.24 for myctophid and nonmyctophid (Ano- 

 plogaster cornuta, Gonostoma elongatum ) fishes, re- 

 spectively, from the eastern Gulf of Mexico (Donnelly 

 and Torres, 1988). Because M. muelleri and both 

 myctophid and nonmyctophid fishes studied by 

 Donnelly and Torres (1988) are diel vertical migra- 

 tors, these greater Q ]0 values suggest that diel fluc- 

 tuations in metabolic rates are associated with daily 

 vertical movements in stratified water. Diel fluctua- 

 tion in metabolic activity associated with diel verti- 

 cal migration was ignored in this study on the 

 premise that daily metabolism of M. muelleri was 

 determined by integrated daily mean temperature 

 ( 12°C ), as has been demonstrated experimentally on 

 the hyperiid amphipod Themisto japoniea, which 

 exhibits an extensive diel vertical migration (Ikeda, 

 1992). 



With regard to the developmental changes in body 

 condition and composition, there are no published 

 data available for comparison with the present data 

 on M. muelleri. However, studies on nonmesopelagic 

 fishes, including red sea bream (Chrysophrys major) 

 by Anraku and Azeta (1973) and walleye pollock 

 (Theragra chalcogramma) by Harris et al. (1986), 

 have demonstrated increases of CFI, C, and caloric 

 contents and decreases in water, ash, and N in asso- 



