548 



Fishery Bulletin 88(3). 1990 



Figure 6 



Fluctuation of the catch of An-tDXcopns japonicus in Akita district, 

 the northern Sea of Japan (after Ikehata 1987). 



only 10'^ tons from the maximum record of about 

 18 000 tons in 1966; the maximum/minimum ratio was 

 about 180. Such drastic fluctuations may be extremely 

 rare among demersal fishes, and a ratio of about 180 

 would be exceptionally great even among pelagic fish 

 stocks (Funakoshi 1988). Usually these fluctuations are 

 attributed to heavy fishing on a parent stock after the 

 appearance of several poor year-classes, or conspicu- 

 ous recruitment success in particular periods (Lasker 

 1981). It is alo generally accepted that success or fail- 

 ure in survival during the early period of ontogeny is 

 critically important for successful year-classes. 



In addition to the early-life-history traits, rearing 

 experiments suggest that early larvae oi A. joponicus 

 have many adaptive features promoting survival. They 

 include an early onset of exogenous feeding paired with 

 a long period of mixed feeding (mixed endogenous and 

 exogenous feeding) in larvae 3 days after hatching to 

 early juveniles of about 20 mm SL (Maekawa 1985). 

 Likewise, Marliave (1981) observed an early onset of 

 first feeding in T. trichodcm, at about 48 hours after 

 hatching in an aquarium. Prolonged mixed feeding is 

 also possible in this species. This may suggest that 

 starvation is not usually the main cause of mortality 

 in early stages. Concerning other mortality factors, 

 such as predation during the early larval period, no 

 reliable information is available for either species. 



The importance of mixed feeding as a feature of a 

 developing organism was stressed by Balon (1986). He 

 suggested that the flexibility provided by a varying 

 duration of mixed feeding can facilitate changes in the 

 entire life history of the species. In view of the char- 

 acteristic mixed-feeding feature of early stages of these 

 two species, their contrasting ontogeny seems to be 

 largely explained within this context. Possibly, slight 



differences in size and yolk volume in newly hatched 

 larvae of the two species are responsible for creating 

 the observed dichotomy in their life history patterns: 

 A. jnponicus developed the indirect type of ontogeny, 

 having a distinct pelagic larval stage and demersal 

 juveniles with intervening metamorphosis; T. trichodon 

 developed the rather direct type of ontogeny having 

 no distinct pelagic larval stage. 



These contrasting life history patterns may be closely 

 associated with the probable differences of their stock 

 sizes. For example, the highly derived nature of ontog- 

 eny in A. japonicus, including the locally restricted 

 spawning grounds, the specialized spawning method, 

 the remarkably precise spawning season, and the typ- 

 ical sequence of early developments, may imply a high 

 likelihood of a greater sensitivity of stock size to en- 

 vironmental changes. Of these features, the presence 

 of so-called "first metamorphosis" (Youson 1988) 

 should be emphasized because this phase, although 

 less drastic than than the others, is expected to play 

 a significant role in regulating successful transition 

 events according to varying environmental situations. 



Acknowledgments 



I would like to thank Drs. J.B. Marliave (Vancouver 

 Aquarium) and T. Minami (Hokkaido Regional Fish- 

 eries Research Laboratory) for making specimens 

 available to me. Dr. Marliave also kindly reviewed the 

 manuscript. Colleagues of the Japan Sea Regional 

 Fisheries Research Laboratory and the Akita Prefec- 

 tural Fisheries Experimental Station kindly helped me 

 in various phases of this study. I am also indebted to 

 Mrs. M. Hara (Ocean Research Institute) for illustrat- 

 ing figures and typing the manuscript. This study was 

 partially supported by a Grant-in-Aid for Scientific 

 Research from the Japan Ministry of Education, 

 Science and Culture (63480067). 



Citations 



Allen, M.J., and G.B. Smith 



1988 Atla.s and zoogeography of common fishes in the Bering 

 Sea and northeastern Pacific. NOAA Tech. Rep. NMFS 6«, 

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 Bailey, J.E., B.L. Wing, and J.H. Landingham 



1983 Juvenile Pacific sandfish, Trirhodoti trichodon, associ- 

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 nearshore area, southeastern Alaska. Copeia 1983:.549-551 . 



Balon, E. 



1981 Additions and amendments to the classification of repro- 

 ductive styles in fishes. Environ. Biol. Fish. 6:377-.389. 



1984 Patterns in the evolution of reproductive styles in fishes. 

 In Potts, C.W., and R.J. Wootton (eds.). Fish reproduction: 

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