635 



Abstract — The annual ovarian cycle, 

 mode of maturation, age at maturity, 

 and potential fecundity of female 

 Rikuzen sole (Dexistes rikuzenius) 

 from the North Pacific Ocean off the 

 coast of Japan were studied by 1) his- 

 tological examination of the gonads, 

 21 measurement and observation of 

 the oocytes, and 3) by otolith aging. 

 The results indicated that ovulation 

 occurs from September to December 

 and peaks between September and 

 October. Vitellogenesis began again 

 soon after the end of the current 

 season. Maturity was divided into 

 eight phases on the basis of oocyte 

 developmental stages. Mature ova- 

 ries contained developing oocytes and 

 postovulatory follicles but no recruit- 

 ing oocytes, indicating that this spe- 

 cies has group-synchronous ovaries 

 and is a multiple spawner. Almost 

 all females matured first at an age 

 of 1+ year and spawned every year 

 until at least age 8+ years. Poten- 

 tial fecundity increased exponentially 

 with body length and the most fecund 

 fish had 15 times as many oocytes as 

 the least fecund fish. Potential fecun- 

 dity and relative fecundity were both 

 positively correlated with age from 1 

 to 6+ years, but were negatively corre- 

 lated, probably because of senescence, 

 in fish over 7 years. These results 

 emphasize that the total productivity 

 of aD. rikuzenius population depends 

 not only on the biomass of females 

 older than 1+ but also on the age 

 structure of the population. 



Reproductive biology of female Rikuzen sole 

 (Dexistes rikuzenius)* 



Yoji Narimatsu 



Daiji Kitagawa 



Tsutomu Hattori 



Tohoku National Fisheries Research Institute 

 Fisheries Research Agency 

 Hachinohe Branch. Same-machi 

 Hachinohe, Aomon, 031-0841 Japan 

 E-mail address (for Y. Narimatsu) nary@aftrc go ip 



Hirobumi Onodera 



Iwate Fisheries Technology Center 

 Hirata, Kamaishi 

 Iwate, 026-0001 Japan 



Manuscript submitted 10 January 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 10 April 2005 by the Scientific Editor. 



Fish. Bull. 10.3:635-647 (2005). 



To understand fish population dynam- 

 ics, reproductive information, such as 

 the maturation of oocytes, the size 

 and age at first maturity, and fecun- 

 dity, is indispensable. Gonadal matu- 

 ration is determined from the external 

 appearance of the gonads, the gonad- 

 osomatic index, and oocyte size, or 

 from observations of histologically 

 prepared gonads (West, 1990). With 

 the former two methods it is possible 

 to measure samples in the field and 

 to record data on numerous samples 

 in a short period of time; however, the 

 mode of oocyte development can only 

 be clarified by using observations of 

 histologically prepared gonads (Wal- 

 lace and Selman, 1981). The methods 

 used to determine if an individual has 

 spawned and to measure the number 

 of eggs spawned in the current repro- 

 ductive season differ with the mode of 

 oocyte development (West, 1990). 



In fishery models, reproductive 

 potentials are conventionally repre- 

 sented by spawning stock biomass 

 (Ricker, 1954; Beverton and Holt, 

 1957; Trippel et al., 1997). Howev- 

 er, at the population level spawning 

 stock biomass does not always corre- 

 late with egg productivity. Length at 

 first maturation, the frequency of oc- 

 currence of degenerated oocytes, and 

 fecundity (that is, the total number 

 of offspring produced in a reproduc- 

 tive season by an individual female) 



are closely related to the age and 

 energetic conditions of an individual 

 (Hunter and Macewicz, 1985a; Hor- 

 wood et al., 1986, 1989; Trippel et 

 al., 1997; Sampson and Al-Jufaily, 

 1999; Kurita et al., 2003). Therefore, 

 examination of age and body size in 

 relation to fecundity is useful in de- 

 termining the abundance of eggs laid 

 in a population. 



Oocyte development can be divided 

 into three types (Wallace and Sel- 

 man, 1981). In determinate fecundity, 

 fecundity is fixed before spawning 

 starts, such as in species which have 

 synchronous or group-synchronous 

 ovaries. In indeterminate fecundity 

 (i.e., for those species whose ovaries 

 develop asynchronously), unyolked 

 oocytes grow to maturity after the 

 onset of spawning (Hunter and Mace- 

 wicz, 1985b; Hunter et al., 1992). In 

 addition, the development of oocytes 

 can vary even among populations of a 

 single species (Sampson and Al-Jufai- 

 ly, 1999) and some females classified 

 as maturing or mature by external 

 observation are often actually imma- 

 ture, and vice versa (Hunter et al., 

 1992; Zimmermann, 1997). Hence, 

 with a species or a population for 



1 Contribution B57 from Tohoku National 

 Fisheries Research Institute, Fisher- 

 ies Research Agency of Japan, Miyagi, 

 Japan. 



