Abstract. — We compai-ed rate 

 of formation of scale circuli and spac- 

 ing between circuli with fish growth 

 rate and scale growth rate in three 

 groups of young coho salmon Onco- 

 rhynchus kisutch): (!) smolts held in 

 saltwater tanks, (2) tagged preco- 

 cious males (jacks) returning to a re- 

 lease facility after only 3 or 4 months 

 in the ocean in two different years, 

 and (3) tagged juvenile coho salmon 

 caught in the ocean. Rate of forma- 

 tion of scale circuli was significant- 

 ly and positively correlated with fish 

 growth rate and with scale growth 

 rate in all groups. However, rate of 

 circulus formation at a given growth 

 rate was lower for large jacks than 

 for the smaller and younger fish held 

 in saltwater tanks, suggesting that 

 rate of circulus formation is nega- 

 tively related to size or age of fish as 

 well as positively related to growth 

 rate. Spacing of circuli was also sig- 

 nificantly and positively correlated 

 with fish growth rate in all but one 

 group of returning jacks, and with 

 scale growth rate in all groups. The 

 relationship between circulus spac- 

 ing and fish growth rate varied 

 among groups, partly because the 

 relationships between scale-radius 

 and fish length and between rate of 

 circulus formation and fish growth 

 rate also varied among groups. Scale 

 circulus spacing could be used to 

 compare growth rates between 

 groups of juvenile coho salmon that 

 are of similar size and age and that 

 have a common relationship between 

 scale radius and fish length. 



Spacing of Scale Circuli versus 

 Growth Rate \n Young Coho Salmon 



Joseph P. Fisher 

 William G. Pearcy 



College of Oceanography, Oregon State University 

 Corvallis. Oregon 97331-5503 



Spacing of scale ridges (circuli) is a 

 potentially valuable tool for compar- 

 ing growth rates of fish where other 

 data are not available. Scale circulus 

 spacing has been found to be positive- 

 ly correlated with fish growth rate in 

 several species of fishes (Doyle et al. 

 1987; Matricia et al. 1989; Glenn and 

 Mathias 1985; Bhatia 1932; Bilton 

 1971a, 1975). Use of scales for study- 

 ing growth has distinct advantages 

 over other methods, such as the spac- 

 ing of daily rings in otoliths, since 

 scales can be easily obtained without 

 killing the fish and are more quickly 

 prepared and read. 



Spacing of scale circuli is detemiined 

 by both the rate at which circuli are 

 formed and the rate of growth of the 

 scale. Whether scale circulus spacing 

 can be used to estimate fish growth 

 rate depends on whether scale growth 

 and circulus deposition rate are re- 

 lated to fish growth rate in a con- 

 sistent, predictable manner. To de- 

 termine the usefulness of circulus 

 spacing for estimating growth rate of 

 juvenile coho salmon, we investigated 

 the relationships between scale radius 

 and fish length, between rate of cir- 

 culus formation and fish and scale 

 growth rates, and between circulus 

 spacing and fish and scale growth 

 rates in three groups of marked 

 young coho salmon: (1) subyearling 

 (age 0) smolts held in saltwater tanks, 

 (2) yearling (age 1.0)* fish returning 



Manuscript accepted 13 July 1990. 

 Fislu'i-y Bulletin, U.S. 88:6.37-643. 



' Age designation follows Koo (1962) and God- 

 frey et al. (197.5), where the number to the 

 left of the decimal indicates the number of 

 winters spent in freshwater, and the number 

 to the right of the decimal the number of 

 winters spent in saltwater. 



as jacks to a coastal hatchery after 

 3 or 4 months in the ocean in two 

 different years, and (3) marked juve- 

 nile coho salmon (age 0.0 and age 

 1.0) caught in the ocean within 2-4 

 months of entering the ocean. Our 

 purpose was to develop a method for 

 comparing growth rates of unmarked 

 juvenile coho salmon caught in the 

 ocean in different years (see Fisher 

 and Pearcy 1988).' 



Methods 



Coho smolts held in 

 saltwater tanks 



Coho smolts (age 0) were collected 

 from one of the raceways at Oregon 

 Aqua Foods, Inc's. Yaquina Bay, 

 Oregon, release facility and trans- 

 ferred to the Hatfield Marine Science 

 Center in July 1982. About 40 fish 

 were placed in each of seven 1.5-m 

 diameter fiberglass tanks. A constant 

 flow of sea water was maintained to 

 each tank. Daily food rations were 

 varied between tanks from 0.6 to 

 3.0% of total salmon biomass in order 

 to produce a wide range of fish 

 growth rates. Fish in five tanks were 

 fed Oregon Moist Pellet, while those 

 in two others were fed thawed frozen 

 euphausiids. Water temperature dur- 

 ing the experiment was variable, 

 ranging from approximately 11° to 

 17°C. 



During 22-24 July, all the fish were 

 anesthetized with MS-222, measured 



Reference to trade names does not imply en- 

 dorsement by the National Marine Fisheries 

 Service, NOAA. 



637 



