Fisheries Science 64(3), 385-387 (1998)

Validity of Age Determination in the Fluvial Japanese Charr leucomaenis by Scale Reading

Tomoyuki Nakamura,*1 Takashi Maruyama,*2 and Seiichi Watanabe*3 *1Nakagawa Branch , Tochigi Prefectural Fisheries Experimental Station, Ogawa, Nasu, Tochigi 324-0501, Japan *2Department of Ocean Sciences , Tokyo University of Fisheries, Konan, Minato, Tokyo 108-8477, Japan *3Department of Aquatic Biosciences , Tokyo University of Fisheries, Konan, Minato, Tokyo 108-8477, Japan (Received September 19, 1997)

The validity of age determination of the Japanese charr Salvelinus leucomaenis using scale read ings was examined by the mark and recapture method in a Japanese mountain stream from 1986 to 1989. When recaptured within a year, all of the 3 (1 growth and 2 resting) scale zone fish were found to still have 3 zones on their scales. One year after marking, they had 4 (2 growth and 2 resting) or 5 (3 growth and 2 resting) zones on their scales and after 2 years, they still had 4 or 5 zones. Fish with 1 rest ing zone, i.e., 1 annulus, were regarded as age 1+ and fish with 2 annuli were regarded as age 2+. Conse quently, age determination of the Japanese charr using scales might be reliable to 1+ age but doubtful for 2+ and older. Key words: Salvelinus leucomaenis, Japanese charr, age determination, scale

Scales, otoliths, fin rays and other skeletal structures Fish were subsequently released at the place of capture. have been used for age determination in fish. Among these, scales have been frequently used because of the con Preparation of scales and scale measurement venience of preparation and observation. However, scales About 10 scales from each fish were soaked in 3% KOH have been shown to yield inaccurate ages for brook water solution for 10min and subsequently rinsed with dis Salvelinus fontinalis,1,2) Atlantic salmon salar,3,4) tilled water. They were then mounted between 2 glass Salmo trutta,4,5) masu salmon slides and dried. Scales were observed with a binocular masou,6) white sucker Catostomus commerson,7) and microscope at 100X magnification and scales with small cir whitefish Coregonus clupeaformis.8) Scales have been used cular or ovular nuclei were regarded as original scales (Fig. for age determination of the Japanese charr Salvelinus leu 1), others as regenerated scales. The original scales were comaenis.9-11)However, Nakamura et al.11)suggested that measured for their nucleus radius and the scale with the the 2+, 3+ and 4+ fish determined by scales might include shortest radius was selected from each fish. The number of some older fish. growth and resting zones were then measured on these The purpose of this study was to examine the validity of selected scales. They were measured along the longest an age determination by scale reading in the Japanese charr. terior axis of scales as shown in several salmonids.2,5,13,14)

Materials and Methods Determination of sex Sex was distinguished by the relationship between stand Study area The mark and recapture experiments were carried out in the middle reaches of the Jadani Stream (upper and mid dle study sections in the previous papers11), central Japan. The stream is a typical Japanese mountain stream and its physical characteristics are given in the previous paper.

Scale sampling A total of 1559 fish were caught by angling in June (late May to mid June), August (late July to mid August) , and N ovember (late October to mid November) from 1986 to 1989. About 20 scales were taken from the fish below the posterior edge of the dorsal fin, 2 to 3 rows above the later al line.12)Each fish was measured for its standard length

(SL) and head length (HL). Individually coded plastic an Fig. 1. Original scale of a Japanese charr 194 mm SL, showing 3 chor tags were attached to the dorsal surface of each fish. growth and 2 resting zones. 386 Nakamura et al. and length and head length for 118 males and 73 females, observed for sperm release or ovulation in November. The relationship between SL and HL was expressed by separate linear equations for males and females. There was a significant difference in the gradient of the 2 equations (ANCOVA, df=1,187, F=11.067, p<0.05). Also the minimum standard length for mature fish was 147 mm in males and 169 mm in females. Consequently, the fish fit ting the requirements given below were regarded as male Fig. 2. Growth of the scale of a Japanese charr with 2 growth and I rest and female, respectively. ing zones at the time of mark and release (left: 2 growth and 1 resting zones in June 1986; middle: 2 growth and 2 resting zones in June Male :HL•†0.30 SL-9.98 for SL•†147 mm 1987; right: 3 growth and 2 resting zones in November 1987). Female :HL•…0.26 SL-5.39 for SL•†169 mm The sex of the fish was distinguished correctly by these in equalities for 98.1 % of males and 97.1 % of females.

Results

Twenty-four 1 zone fish (fish with only 1 growth zone on their scales) were marked and released during the study period and 1 fish which was marked in November 1988 was recaptured in August 1989. The number of scale zones of this fish had increased to 3 (2 growth and 1 resting zones) at recapture. Twenty-two male and 5 female 3 zone fish were recap tured within the year in which they were marked and released. When recaptured within a year, all of the 3 zone fish were found to still have 3 zones. Thirty-five male and 29 female 3 zone fish were recap tured in the following 3 years after they were marked. Fig. 3. Seasonal and annual changes in the number of growth and rest ing zones on the scales of Japanese charr with 3 zones (2 growth and Four (2 growth and 2 resting) or 5 (3 growth and 2 resting) 1 resting) at the time of mark and release. zones were observed on their scales after 1 year for both sexes (Fig. 2). The ratio of 5 zone fish increased from 6.7% in June to 63.6% in November for males, and from 50.0% in June to 75.0% in November for females (Fig. 3). After 2 years, 4 or 5 zones were still observed in males while only 5 zones were observed in females. The ratio of 5 zone fish in females was significantly higher than in males in June 1 year later (X2=4.457, df=1, p<0.05) and June 2 years later (X2=4.273, df=1, p<0.05). After 3 years, 4 or 6 (3 growth and 3 resting) zones were observed in males and 5 zones were observed in females. Twenty-five male and 18 female 4 zone fish were recap tured in the following 3 years after they were marked. Af ter 1 year, 4 or 5 zones were observed on the scales of both sexes and the ratio of 5 zone fish ranged from 15.4% to 40.0% in males, and 66.7% to 75.0% in females (Fig. 4). The ratio of 5 zone fish in females was significantly higher than in males in June 1 year later (ƒÔ2=4.031, df=1, Fig. 4. Seasonal and annual changes in the number of growth and rest p < 0.05). For both sexes, 4 to 6 zones were observed on their ing zones on the scales of Japanese charr with 4 zones (2 growth and scales after 2 years. 2 resting) at the time of mark and release.

Discussion

In the present study, within a year of marking, all of the for 0+ fish in the present study. However, the number of 3 (2 growth and 1 resting) zone Japanese charr still had 3 scale zones of a 1 zone fish, i.e., 0+, marked in November zones on their scales, and after 1 year they had 4 (2 growth increased to 3 zones by August of the following year and and 2 resting) or 5 (3 growth and 2 resting) zones. scale readings were generally available for younger fish (0+ However, after 2 years they still had 4 and 5 zones. The and 1+) of many salmonids in age determination2,3,5,15). fish with a resting zone, i.e., I annulus, were generally re Consequently, age determination of Japanese charr by garded as age 1 + and fish with 2 annuli were regarded as scale reading might be reliable to 1 + but doubtful for 2+ age 2+. There is little quantative data on the scale growth and older. Age Determination in the Japanese Charr 387

There are many papers referring to the difficulties of age trout, , and . Trans. Am. Fish. Soc., 83, determination by scale reading in salmonids. McFadden15) 91-103 (1953). showed that it was more difficult to read ages on scales 3) K. A. Havey: Validity of the scale method for aging hatchery from older brook trout (3+) than younger fish (1+ and 2+) reared Atlantic salmon. Trans. Am. Fish. Soc., 88, 193-196 using mark and recapture experiments and he pointed out (1959). 4) A. J. Jensen and B. O. Johnsen: Difficulties in aging Atlantic that the resting zones, i.e., annuli, were formed by larger salmon (Salmo salar) and brown trout (Salmo trutta) from cold fish within the same age group. Alvord2) showed that the rivers due to lack of scales as yearlings. Can. J. Fish. Aquat. Sci., annuli did not completely form seasonally and annually 39, 321-325 (1982). for older brown trout and he suggested that slow body 5) B. Jonsson: Comparison of scales and otoliths for age determina growth might cause the unsuccessful zone formation on tion in brown trout, Salmo trutta L. Nor. J. Zool., 24, 295-301 scales. Jonsson5) found that the scale zones were not (1976). 6) K. Kiso: The life history of masu salmon Oncorhynchus masou formed for several mature brown trout and he suggested originated from rivers of the Pacific coast of northern Honshu, that unsuccessful zone formation on scales in mature fish Japan. Bull. Natl. Res. Inst. Fish. Sci., 7, 1-188 (1995). might be caused by slow growth at older ages. In the 7) R. J. Beamish and H. H. Harvey: Age determination in the white present study, zone formation on scales of the Japanese sucker. J. Fish. Res. Bd. Can., 26, 633-638 (1969). charr was less successful for 3+ and older fish than 8) K. H. Mills and R. J. Beamish: Comparison of fin-rays and age de younger fish. Body growth of the Japanese charr became termination for lake whitefish (Coregonus clupeaformis) and their slow at 3+ and older in the Jadani Stream (Nakamura, un implications for estimates of growth and annual survival. Can. J. Fish. Aquat. Sci., 37, 534-544 (1980). publ. data). So, the unsuccessful zone formation might be 9) M. Oshima: Review of the charr found in the Japanese waters, with caused by slow scale growth that resulted from slow body description of one new species. Botany and Zoology. 6, 1-7 growth at older ages. Zone formation was also less success (1938) (in Japanese). ful for the 2+ and older males than the same age females. 10) F. Kato: Ecological and morphorogical notes on the chary, Salveli The results suggested that body growth of Japanese charr nus leucomaenis in the Nagara River and Ibi River systems. Suisan might be slower for males than females at older ages. zoshoku, 40, 145-152 (1992). However, no significant differences were found in the body 11) T. Nakamura, T. Maruyama, and E. Nozaki: Seasonal abundance and the re-establishment of iwana charr Salvelinus leucomaenis f. growth between sexes,16) so relative unsuuccessful zone for pluvius after excessive sediment loading by road construction in the mation on scales of males could not be explained by the Hakusan National Park, central Japan. Envir. Biol. Fish., 39, 97 differences in body growth. Absorption was often found 107(1994). on fish scales during the spawning season17) and there 12) International North Pacific Fisheries Commission: Proceedings of might be differences in scale absorption between males and the Annual Meeting 1957, pp. 70-73 (1957). 13) H. T. Bilton, D. W. Jenkinson, and M. P. Shepard: A key to five females. However, there is little quantative data on scale species of Pacific salmon ( Oncorhynchus) based on scale absorption caused by spawning or maturation for character. J. Fish. Res, Bd. Can., 21, 1267-1288 (1964). Japanese charr. Further studies are expected to show 14) F. Kato: Notes on the life history of lake-run specimens of the ama whether scale absorption occurs for Javanese charr or not. go salmon, Oncorhynchus ishikawae. Suisanzoshoku, 39, 61-69 Otoliths have been frequently used for age determina (1991). tion in Japanese charr in recent studies.16,18-21) The age of 15) J. McFadden: Relationship of size and age to time of annulus for fish may be estimated more accurately using otoliths rather mation in brook trout. Trans. Am. Fish. Soc., 88, 176-177 than scales as shown for white sucker7,12) and lake (1959). 16) S. Yamamoto, S. Nakano, and K. Tokuda: Variation and diver whitefish,8) however the fish must be killed to remove gence of the life-history of Japanese charr Salvelinus leucomaenis in otoliths. Consequently, to obtain ecological and behav an artificial lake-inlet stream system. Jpn. J. Ecol., 42, 149-157 ioral information related to ages on Japanese charr, we (1992). should use fish of known age, such as hatchery-reared fish 17) I. Kubo and T. Yoshiwara: Fishery Biology, Kyoritsu Publishing or fish caught at the latest age of 1 + and individually Corporation, Tokyo, 1957, p.482 (in Japanese). marked. 18) S. Nakano, K. Maekawa, and S. Yamamoto: Change of the life cy cle of Japanese charr following artificial lake construction by dam ming. Nippon Suisan Gakkaishi, 56, 1901-1905 (1990). Acknowledgments We wish to express our sincere thanks to emeritus 19) H. Kimoto: The stock of gogi-char Salvelinus leucomaenis imbrius professor Dr. K. Takagi, Tokyo University of Fisheries, for his helpful in Shiso River in Shimane Prefecture. Nippon Suisan Gakkaishi, 58 suggestions and encouragement. We are also grateful to Mr. A. Mizuno, (9), 1585-1593 (1992). Mr. E. Nozaki, and their colleagues at the Ishikawa Prefectural Hakusan 20) S. Yamamoto and S. Nakano: Growth and development of a bi Nature Conservation Center and Mr. A. Mori, Mr. M. Aoki, and Mr. T. modal length-frequency distribution during smolting in a wild popu Hosoda for their helpful assistance during our work in the Jadani lation of white-spotted charr in northern Japan. J. Fish. Biol., 48, Stream. We thank two anonymous reviewers of this paper for their criti 68-79 (1996). cal comments and useful suggestions . 21) S. Yamamoto, Y. Takahashi, S. Kitano, and A. Goto: Residual fe male part in an anadromous population of white-spotted charr, Sal References velinus leucomaenis, in Southern , Japan. Jpn. J. Ichthyol., 43, 101-104 (1996). 1) W. King: Trout management studies at Great Smoky Mountains Na 22) R. J. Beamish: Determination of age and growth of populations of tional Park. J. Wildlife Management, 6, 147-161 (1942). the white sucker (Catostomus commersoni) exhibiting a wide range 2) W. Alvord: Validity of age determinations from scales of brown in size at maturity. J. Fish. Res. Bd. Can., 30, 607-616 (1973).