Abstract. - A biochemical exam- 

 ination of otolith growth-somatic 

 growth relationship was conducted 

 in rainbow trout Oncorhynchus my- 

 kiss. The rate of otolith growth was 

 defined by calcium deposition on oto- 

 liths in an in vitro isolated prepar- 

 ation of otolith-containing sacculi. 

 Somatic growth was estimated by 

 RNA-DNA ratios in white trunk 

 muscle. Rainbow trout weighing ap- 

 proximately 120 g were starved for 

 5 days and then fed commercial trout 

 pellets once a day. They were sam- 

 pled on days 1, 2, 3, and 5 after star- 

 vation, and on days 1, 2, 3, and 4 

 after feeding. In a separate experi- 

 ment, fish were sampled at 6-hour in- 

 tervals of 1000, 1600, 2200, and 0400 

 hours over a 24-hour period. Otolith 

 and somatic growth showed a posi- 

 tive relationship, both decreasing 

 from 2 days after starvation and re- 

 covering on day 4 after feeding. In 

 otoliths, however, the starvation-in- 

 duced decrease in calcium deposition 

 was transiently restored on day 1 

 after feeding, followed by a decrease 

 on day 2. The diel relationship be- 

 tween otolith and somatic growth 

 was coupled, showing minimum 

 levels at 2200 hours. These results 

 suggest that otolith growth ordinar- 

 ily reflects somatic growth rates on 

 the daily basis. 



Biochemical Relationship 

 Between Otolith and Somatic 

 Growth \n the Rainbow Trout 

 Oncorhynchus my kiss: 

 Consequence of Starvation, 

 Resumed Feeding, and Diel Variations 



Yasuo Mugiya 

 Hirotaka Oka 



Faculty of Fisheries, Hokkaido University 

 Mmato-3. Hakodate 041, Japan 



Manuscript accepted 17 December 1990. 

 Fishery Bulletin, U.S. 89:239-245 (1991). 



Teleost otoliths are calcium carbon- 

 ate concretions which have incre- 

 ments consisting of a bipartite struc- 

 ture of light and dark rings. These 

 structures are known to be formed on 

 a daily basis (Pannella 1971). Since 

 otolith and fish size are highly cor- 

 related for a variety of marine and 

 freshwater species (Campana and 

 Neilson 1985), it is possible to esti- 

 mate growth-rate histories of individ- 

 ual fish by measuring the width of 

 otolith increments. Volk et al. (1984) 

 averaged otolith increment widths 

 over each week and found a linear 

 regression of mean increment width 

 with somatic growth rate in chum 

 salmon Oncorhynchus keta under 

 controlled feeding. Nishimura and 

 Yamada (1988) successfully back- 

 calculated the growth rate of walleye 

 pollock Theragra chalcogramma by 

 using mean otolith width measured 

 every 10 increments. However, it re- 

 mains to be shown whether the rate 

 of otolith growth reflects somatic 

 growth rates in terms of daily or sub- 

 daily trends. 



Recently several workers (Secor 

 and Dean 1989, Reznick et al. 1989, 

 Wright et al. 1990) reported an un- 

 coupling of the relationship between 

 otolith and somatic growth in fish 

 populations experiencing slow and 

 fast somatic growth. Similar uncou- 



pling was exaggeratedly induced in 

 hypophysectomized goldfish Caras- 

 sius auratus, in which somatic growth 

 in length was completely inhibited 

 but otolith continued to grow at a re- 

 duced rate (Mugiya 1990). 



Since the otolith (sagitta) occurs 

 within the sacculus which is anatom- 

 ically closed in rainbow trout Onco- 

 rhynchus mykiss, it is feasible to take 

 out the otolith-containing sacculus 

 without any leakage of the endolymph 

 (Mugiya 1984). An in vitro prepara- 

 tion of the isolated sacculi was used 

 for indicating the current growth 

 rate of otoliths, which reflected the 

 in vivo physiological state at the time 

 when the fish were sampled (Mugiya 

 1984, 1987). Somatic growth is a 

 balance between catabolic and ana- 

 bolic components in protein meta- 

 bolism (Miglavs and Jobling 1989). 

 Since accretive growth should be 

 directly associated with protein syn- 

 thetic capacity, RNA-DNA ratios in 

 muscle are widely used as an indi- 

 cator of the short-term or current 

 somatic growth rate (Bulow 1987). 



The aim of the present study is to 

 clarify the biochemical relationship 

 between otolith and somatic growth 

 on a daily basis, using starved and 

 then fed rainbow trout. The otolith 

 growth-fish growth relationship was 

 also examined at 6-hour intervals 



239 



