50 



Fishery Bulletin 94( 



1996 



through oxygen consumption in cells is mediated 

 mostly by the formation of adenosine triphosphate 

 (ATP), and this oxidative phosphorylation is driven 

 by ETS that is embedded in the inner membrane of 

 eukaryotic mitochondria and in the cell membrane 

 of prokaryotes (cf. Packard, 1985). The ETS assay 

 was first introduced for the study of plankton respi- 

 ration (Packard et al., 1971, 1975), and additional 

 data have been accumulated (Packard, 1985). Al- 

 though application of this assay to fish respiration 

 is currently limited to only a few studies ( Ikeda, 1989; 

 Yamashita and Bailey, 1990), this method is advan- 

 tageous in that incubation of live specimens is not 

 necessary, and it is almost free from the effect of 

 physiological stress incurred during capture of fish 

 in the field. The ETS activity represents a potential 

 rather than an actual oxygen consumption rate. In 

 this respect, the ratio of ETS activity to respiratory 

 oxygen consumption is known to be quite constant 

 across various systematic groups of animals (King 

 and Packard, 1975). The biochemical basis of the ETS 

 assay and the rationale for the estimation of respi- 

 ratory oxygen consumption rates are detailed in 

 Packard (1985). 



In the present study, ETS activity was determined 

 and used as a basis to estimate respiratory oxygen 

 consumption rates of M. muelleri from the Sea of Ja- 

 pan. The chemical composition of fish and gonads at 

 various developmental stages was determined. These 

 metabolic and chemical composition data were com- 

 bined with natural growth rate data to establish an 

 energy budget pattern for M. muelleri over its lifetime. 



Materials and methods 



face, measured for body length, and were frozen 

 (<-20°C). Total length (TL: from tip of the snout to 

 end of the tail), instead of standard length (SL), was 

 used throughout this study to facilitate work on ship- 

 board. For conversion of TL to SL the equation SL = 

 0.82271, + 0.161 may be used (Ikeda, 1994). 



Metabolism 



ETS activity was measured in individual fish within 

 two weeks after collection by the modified tetrazo- 

 lium reduction method (Owens and King, 1975). The 

 general procedure of ETS assay for fish samples is 

 described elsewhere (Ikeda, 1989). No significant loss 

 of ETS activity during storage for 36 days at 

 -20°C has been reported for two fish species (Ikeda, 

 1989). The homogenates were incubated at 12"C, the 

 estimated daily mean temperature encountered by 

 M. muelleri during their diel vertical migration. In a 

 separate test, the effect of temperature on ETS ac- 

 tivity was assessed at six temperatures (0.5°, 4°, 8°, 

 12°, 16°, and20°C). 



For the conversion of ETS activity to actual respi- 

 ratory oxygen consumption (R), ETS/R = 2 was pro- 

 posed on the assumption that Michaelis-Menten ki- 

 netics could be applied to respiratory chemistry and 

 that the concentration of the respiratory regulator 

 (i.e. ADP) was maintained near the Km (cf. Packard, 

 1985). The ETS:R ratios obtained directly from crus- 

 tacean plankton and fishes are close to this theoreti- 

 cal value (Table 1). Hence, ETS/R = 2 was used to 

 convert ETS to R in this study. 



Oxygen consumption was converted to caloric units 

 by using the equivalent of 4.80 cal/mL 2 (Gnaiger, 

 1983). 



Fish 



Fishes were collected from Toyama Bay and Sado 

 Strait (both within the southern Sea of Japan) and 

 from waters around Yamato Rise (central Sea of Ja- 

 pan) aboard the RV Mizuho-Maru from September 

 1988 through September 1992. Collections were 

 made at night with a 2-m Isaacs-Kidd midwater trawl 

 (1.5 mm mesh) which was towed obliquely from 100- 

 250 m depths to the surface. Fish-larvae nets (0.5 

 mm mesh) were used to collect larvae and small ju- 

 veniles. For the collection of specimens used for the 

 ETS assay, the trawl and nets were towed slowly ( 1.5 

 knots) for a short time period ( 10 min) to avoid dam- 

 age to the specimens. Immediately following net re- 

 trieval, fishes in the codend were transferred to a 

 bucket filled with seawater. For body composition 

 analyses and ETS assay, specimens were placed on 

 filter paper to remove excess water on the body sur- 



Condition factor index and body 

 composition 



Condition factor index (CFI) was defined as wet 

 weight (WW) x 10 3 /(TL) 3 for this study. 



Frozen specimens were weighed (WW in mg) and 

 then freeze-dried, dried further at 60°C for 5 hours 

 to remove residual water, and then weighed (DW in 

 mg). Dried specimens were pooled on the basis of TL 

 into eight size groups (<10, 10 to <15, 15 to <20, 20 

 to <30, 30 to <40, 40 to <50, 50 to <60, and >60 mm 

 TL) and were ground into a fine powder with a ce- 

 ramic mortar and pestle. No separation by sex was 

 made. However, adult males are known to be 35 to 55 

 mm TL in the Sea of Japan (Ikeda, 1994), therefore 

 some males may have been included in the 30 to <40 

 mm, 40 to <50 mm, and 50 to <60 mm TL groups but 

 none in the >60 mm TL group. Powdered samples were 

 used for elemental analyses and ash determinations. 



