56 



Fishery Bulletin 94(1). 1996 



ciation with growth of these fishes. Although neither 

 of these previous studies on nonmesopelagic fishes 

 included adult individuals, the general patterns of 

 change in body condition and composition over the 

 course of growth are consistent with those observed 

 in M. muelleri. Progressive accumulation of lipid in 

 the body is thought to be the cause of these develop- 

 mental changes in CFI, elemental composition, and 

 caloric content (Anraku and Azeta, 1973; Harris et 

 al., 1986). Accumulation of lipid around the diges- 

 tive tract, gonads, and liver was confirmed for ma- 

 ture adults of M. muelleri in the present study, sup- 

 porting the idea that accumulation of body lipid re- 

 sults in the other changes noted. 



On the basis of analyses of 37 fish species of mixed 

 ages and living at various depths off southern Cali- 

 fornia, Childress and Nygaard ( 1973) concluded that 

 deeper living fishes are characterized by higher wa- 

 ter and lower caloric contents. Compared with the 

 results of Childress and Nygaard (1973), the present 

 data on water and caloric contents of M. muelleri fall 

 somewhere between those living in epipelagic and 

 mesopelagic zones off southern California. Thus, the 

 general bathymetric level at which the population of 

 M. muelleri lives, extrapolated from body composi- 

 tion data, is in general agreement with direct field 

 observation (50 to >150 m depth, Hamano et al., 

 1992). 



Childress et al. (1980) compared life history pat- 

 terns among epipelagic, mesopelagic, and bathype- 

 lagic fishes off southern California and indicated that 

 epipelagic species had the highest growth rates, 

 mesopelagic species the lowest, and bathypelagic 

 species were intermediate. In terms of energy bud- 

 get, deeper living species are characterized by higher 

 lifetime averages of K 2 . In calculating energy bud- 

 gets, Childress et al. (1980) assumed size-indepen- 

 dent M, so that the present results of size-indepen- 

 dent M for M. muelleri can be compared directly with 

 their results. This comparison revealed that K 9 of 

 M. muelleri (17%) is much higher than that of epipe- 

 lagic fishes (3% ) but falls within the range of meso- 

 pelagic fishes ( 15-26%) off southern California. The 

 lifetime average of daily ration F' estimated by 

 Childress et al. (1980) is 3.3 for epipelagic, 0.79 for 

 mesopelagic, and 0.62% for bathypelagic fishes (re- 

 calculated by using the assimilation efficiency of 80% , 

 instead of 73% ). The present estimated lifetime av- 

 erage ofF' (2.9%) forM. muelleri is higher than me- 

 sopelagic F', and closer to the epipelagic F' given by 

 Childress et al. (1980). Greater F' in M. muelleri is a 

 result expected from higher metabolic activities of 

 this fish compared with mesopelagic fishes off south- 

 ern California. As a mesopelagic fish in the Sea of 

 Japan, M. muelleri is different from mesopelagic 



fishes off southern California in that the former is 

 much smaller in size (53 mm TL or 44 mm SL vs. 

 72-118 mm SL) and shorter lived (1.8 yr vs. 5-7.5 

 yr) than the latter. Energy budget comparison indi- 

 cates thatM. muelleri is a more active swimmer (has 

 a higher metabolic activity), thereby consuming more 

 food than those off California, although net growth 

 efficiency is identical between the two. A general 

 implication gained from these comparisons is that 

 M. muelleri in the Sea of Japan are more efficient 

 mediators in energy flow and matter cycling in the 

 pelagic ecosystem than are mesopelagic fishes off 

 southern California. 



Caloric contents of ovaries and testes of the Pa- 

 cific sardine {Sardinops eaerulea) have been reported 

 as 5.43 and 4.85 Kcal/g DW (Lasker, 1970), both of 

 which are greater than the respective values for M. 

 muelleri (4.89 and 4.79 Kcal/g DW, cf. Table 3). Ca- 

 loric content of mature oocytes, instead of intact ova- 

 ries, of M. muelleri is comparable to that of the Pa- 

 cific sardine. Lasker (1970) estimated the energy 

 investment in reproduction to be only 2% of assimi- 

 lated energy. The energy partitioned for reproduc- 

 tion in M. muelleri, on the basis of the maximum 

 gonad index, is 1.3% of the assimilated energy of 1.8- 

 yr-old fish for females and 0.6% for males in this 

 study. The presence of different size groups of yolked 

 oocytes in the ovaries has been observed for M. 

 muelleri from various geographical locations includ- 

 ing the Sea of Japan, and is considered to be evi- 

 dence of multiple or serial spawning (Okiyama, 1971; 

 Gjosaeter, 1981; Yuuki, 1982; Melo and Armstrong, 

 1991; Prosch, 1991). From this view, the present es- 

 timations of energy partition to reproduction in this 

 fish are conservative ones, but the lack of informa- 

 tion about spawning frequency prevents quantita- 

 tive calculation at present. When the spawning fre- 

 quency and the number of eggs released at each 

 spawning become known for M. muelleri in future 

 studies, the reproductive effort of the females will 

 be better defined with the data for caloric content of 

 oocytes given in this study. 



Acknowledgments 



I am grateful to C. B. Miller for critically reading the 

 manuscript and for valuable comments. I thank two 

 anonymous referees for comments that improved the 

 text. Thanks are extended to T Nagasawa for elemen- 

 tal analysis, T Nagasawa and N. Nakao for provid- 

 ing some specimens used in this study, and K. 

 Hirakawa and N. Iguchi for their help in field sam- 

 plings. This research was supported by the fund "En- 

 couragement of Basic Research at the National Re- 



