Aquacult. Sci. 66（2），123－131（2018）

Reproductive biology of a boreal Nemacheilid loach Barbatula oreas introduced into a temperate river in central ,

1,＊ 2 Rui Hatakeyama and Tadashi Kitano

Abstract: The reproductive traits of Barbatula oreas were examined in a population established in the Kaname River, Kanagawa prefecture. Males exhibited unclear seasonal patterns in their monthly mean gonadosomatic index (GSI), and discharged semina from their genital ducts throughout the year. Females exhibited obvious seasonal patterns in the monthly mean GSI, which was higher in spring (March-April) and lower in summer (July-August). Ovarian maturity was divided into three developmental phases (resting, vitellogenic and maturation), and the ovaries in the maturation phase, which had the characteristics of ovaries in the spawning season, were observed from March to July. Post-ovulatory follicles were found even in the ovaries of small fish (< 100 mm SL), indicating spawning at age-1. Total fecundity was 1,049-10,671 per ovary, increasing exponentially with the increasing SL. It was considered that vitellogenesis occurred at a wide range of water temperatures and day lengths (7.5-20.8°C, 9 h 47 min-14 h 33 min), and spawn- ing season began when there was a transition to a suitable spawning temperature (10.2-18.5°C). This population, which matured at age-1, seemed to have a higher intrinsic rate of natural increase compared to a native population.

Key words: Barbatula oreas; Acclimatization; Alien species; Gonadal maturity

Fukudojo, Barbatula oreas is a boreal loach with native fish, including commercial species, belonging to the family Nemacheilidae, and because it feeds on benthos such as aquatic is naturally distributed in , Japan insects (Miyadi et al. 1963), hides under stones (Kottelat 2012). The distributional areas of B. during the daytime (National Institute for oreas have expanded rapidly to lower latitudinal Environmental Studies 2005), and tends to be rivers, such as the , , the dominant species in its natural and invasive , and in northeastern ranges (Nogami et al. 2001; Nagasawa et al. Honshu, Japan, probably due to the release 2009; Hatakeyama et al. 2017). Knowledge of of salmonid seed (Toujo and Hosoya 1998; reproduction in this species, in addition to feed- Ministry of Land, Infrastructure, Transport and ing and behavior, is essential for an appropriate Tourism 2007). In recent years, B. oreas have assessment of ecological impact. also established in the upstream Kaname River The objective of the present study was to clar- in central Honshu (Yashima et al. 2011), which ify firstly, the environmental conditions in which is the lowest latitude river invaded by this the gonadal maturity of B. oreas progresses, and species. therefore in which river environments there There are many unclear aspects regarding is the potential to reproduce, and secondly, to the ecological impact of B. oreas establishment. identify the reproductive traits of B. oreas estab- Barbatula oreas may compete for food or habitat lished in a temperate river.

Received 16 November 2017; Accepted 30 May 2018. 1 Civil Engineering and Eco-Technology Consultants Co., Ltd., 2-23-2 Higashiikebukuro, Toshima, Tokyo 170-0013, Japan. 2 School of Humanities and Culture, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan. ＊Corresponding author: Tel, (+81)3-3988-2634; Fax, (+81)3-3988-3885; E-mail: [email protected] (R. Hatakeyama). 124 R. Hatakeyama and T. Kitano

In the present study, the scientific name, B. GSI = 100 × GW/BW. oreas, was used according to Kottelat (2012), who reviewed the confused taxonomy and nomen- Sexing fish, including the yearling, were clature of loaches, a suborder of Cobitoidei, used for analyzing gonadal maturity and annual although names such as B. toni toni (Miyadi et reproductive cycle, because the gonads of year- al. 1963), B. toni (Nakamura 1984), Noemacheilus ling fish developed rapidly (Hatakeyama et al. toni (Saito 1988), N. barbatulus toni (Masuda and 2017), suggesting spawning at age-1. Males, col- Kobayashi 1994) and Nemacheilus barbatulus toni lected after April 2014, were examined with the (Hosoya 2013) were used hitherto. naked eye whether semen was discharged from the genital duct upon pressing the abdomen. Materials and methods Female fish gonads were monitored by record- ing external features such as color, and oocyte Fish collection and environmental data diameters; the gonads were photographed Specimens were collected from a 1 km section using a digital camera, and then preserved in upstream of the Kaname River in central Honshu, 70% ethanol after fixation in 10% neutral forma- Japan (35°23′24″N, 139°13′36″E). Sampling was lin or Bouinʼs solution for 24 h. Some ovaries conducted once a month, from April 2012 to fixed in Bouinʼs solution were embedded in August 2015. Collection was by scooping with hand paraffin, sagittally sectioned at 4 μm thickness, nets from April 2012 to May 2013, and in conjunc- and stained with Mayerʼs hematoxylin-eosin. tion with an electric shocker (LR-20B: Smith-Root, The developmental stages of germ cells were USA) from June 2013 to August 2015. During the observed under an optical microscope. sampling period, a data logger (UA-002-64: Onset Some ovaries fixed in 10% neutral formalin Computer Co., USA) was placed in the water, were used to estimate the number of oocytes and temperature data recorded every hour to and their diameters. Oocytes weighing approx- be calculated as daily mean water temperature. imately 1/5th of the ovary weight were laid Day length data was obtained from Yokohama, out on a 1 × 1 mm mesh on a petri dish and Kanagawa Prefecture, Japan, which was the near- photographed by a digital camera, and the est monitoring site to the Kaname River (National numbers and diameters were measured using Astronomical Observatory of Japan 1994). image analysis software (JCAM software: J-SCOPE, Japan). Total fecundity (TF) (Hunter Fish measurements and data analysis et al. 1992), which was the standing stock of The collected fish were anesthetized with advanced yolked oocytes in the ovary, was cal- MS-222 in a laboratory and the standard length culated by gravimetric method as follows: (SL) and body weight (BW) measured. Sex was TF = GW × C, basically identified from the pectoral fin-shape according to Ikeda (1936). In fish in which the where C is oocyte density (number of advanced secondary sex characteristics of the fin were oocytes per gram of ovarian tissue). For compar- undeveloped, sex was identified by checking the ison with the native population, TF of fish in the gonads under a stereomicroscope. Fish having Komaoi River, Hokkaido, was also calculated for translucent and string-like gonads and no visi- some ovaries, which were removed from speci- ble oocytes were treated as sexually unidenti- mens collected by Hatakeyama et al. (2017). fied. Fish having slightly clouded and enlarged gonads with no visible oocytes, and fish having Results visible oocytes, were treated as male and female, respectively. In all fish, the gonads were removed Gonadal maturity and annual reproductive cycle and the gonadal weight (GW) measured. As an A total of 462 fish had SLs ranging from 53.6- index of gonadal development, the gonadoso- 149.4 mm (Fig. 1). The GSI was 0.1-1.2 in sex- matic index (GSI) was calculated as follows: ually unidentified (53.6-91.1 mm SL, n = 25), Reproductive biology of Barbatula oreas 125

160

140

(mm) 120 th 100

80

Standard leng 60

40 AM JJASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JA 2012 2013 2014 2015 Fig. 1. Standard length of Barbatula oreas collected monthly in the present study. ⃝, male (n = 201); ×, female (n = 236); ⃝, unidentified (n = 25).

100 665949810 675665445 developmental phase, histological characteris- tics and frequency distribution of oocyte diame-

(%) ters were investigated. y (1) Vitellogenic phase: GSI was 3.9-27.1 (n 50 = 108) (Fig. 3). The ovaries were enlarged and frequenc light yellow in color, and large oocytes (290- 850 μm, n = 200) were visible and densely Relative distributed (Fig. 4a). Ovaries observed histolog- 0 AM JJASOND JFMAMJ JA ically had oocytes at the tertiary yolk stage or 2014 2015 lower (120.0-134.5 mm SL, GSI = 4.8-15.9, n = Fig. 2. Monthly changes in relative frequency (%) of male Barbatula oreas discharging clouded semen from the gen- 4) (Fig. 4b). The ovaries in this phase had one ital duct. , with semen; , without semen. The Arabic or two modes in oocyte diameter (Fig. 5a, b); an numerals indicate the number of individuals. ovary in November had one oocyte group con- sisting of oocytes at the tertiary yolk stage and 0.2-2.8 in males (76.5-148.8 mm SL, n = 201) and lower, but an ovary in February had another 0.4-27.1 in females (67.5-149.4 mm SL, n = 236). advanced group (> 600 μm in oocyte diameter) The monthly mean GSI in males varied consisting of oocytes at the tertiary yolk stage, between 0.8 and 2.1, with unclear seasonal pat- even though two oocyte groups having each terns. Semina from genital ducts (84.4-139.3 mm mode were not completely separated in terms SL, n = 71) were observed throughout the year, of oocyte diameter (Fig. 5b). The ovaries in but relative frequency was greater than 60% in the vitellogenic phase were defined as being in all months from autumn to spring (April-May a state in which oocyte development was pro- 2014, November 2014-May 2015) (Fig. 2). gressing toward the next spawning season. The monthly mean GSI in females varied (2) Maturation phase: GSI was 4.3-24.0 (n = seasonally between 1.9 and 19.4. The mean GSI 61) (Fig. 3). The ovaries in the final maturation was the highest in March (2013 and 2014) and or ovulation were enlarged, transparent and April (2015), and the lowest in July (2012) and light orange in color, and the oocytes were not August (2013 and 2015) (Fig. 3). The mean GSI clearly visible (Fig. 4c). The ovaries that had in December 2012 and January 2015 reached spawned at least once were more deflated than 84.7% and 91.0% of the peak values in 2013 and those in the most enlarged state of the vitello- 2015, respectively. The mean GSI decreased genic phase, with large, clearly visible oocytes rapidly to less than half the peak value in May (350-970 μm, n = 172) (Fig. 4e) that were (2013 and 2015) and June (2014). light yellow in color and sporadically distrib- Ovarian maturity was divided into three uted. The ovaries in this phase had two modes developmental phases as follows on the basis of in oocyte diameter, even though two oocyte the exterior features. In some ovaries in each groups having each mode were not completely 126 R. Hatakeyama and T. Kitano

30

x 25

inde 20 15

10

Gonadosomatic 5

0 AM JJASOND JFMAM JJASOND JFMAMJ J ASOND JFMAMJ JA 2012 2013 20142015

Fig. 3. Monthly changes in the gonadosomatic index in Barbatula oreas. ⃝, vitellogenic phase (n = 108); ×, maturation phase (n = 61); ⃝, resting phase (n = 67). The symbols with vertical bars indicate means ± standard deviations.

a e

10 mm 10 mm

b f

tys

tys pys

yvs

500 μm 500 μm c g

10 mm 5mm d h

pys ar

yvs

pns

mns sys 500 μm 500 μm

Fig. 4. The ovaries in the three developmental phases of Barbatula oreas. (a) exterior of the ovary in the vitellogenic phase (120.0 mm SL, GSI 15.9, January 2013); (b) histological features of the ovary of (a); (c) exterior of the ovary in the maturation phase, during final maturation (111.3 mm SL, GSI 4.3, April 2014); (d) histological features of the ovary in the maturation phase, during final maturation, with oocytes in the migratory nucleus stage (95.0 mm SL, GSI 5.9, June 2014); (e) exterior of the ovary in the maturation phase (134.6 mm SL, GSI 6.5, June 2013); (f) histological features of (e) with post-ovulatory follicles; (g) exterior of the ovary in the resting phase (128.3 mm SL, GSI 1.0, July 2014); (h) histological features of (g). Abbreviations: ar, atresia; mns, migratory nucleus stage; pns, perinucleolus stage; pys, primary yolk stage; sys, secondary yolk stage; tys, tertiary yolk stage; yvs, yolk-vesicle stage. Arrowheads indicate post-ovulatory follicles. Reproductive biology of Barbatula oreas 127 separated (Fig. 5c); in ovaries observed histo- (Fig. 3). The ovaries had the most shrink- logically (89.9-134.5 mm SL, GSI = 5.9-9.6, n age among the three developmental phases = 9), the advanced oocyte group consisted of (Fig. 4g), and were transparent and orange. oocytes at the tertiary yolk stage and higher, The oocytes were not clearly visible but a few and the other group consisted of oocytes at the atresias (230-650 μm, n = 30) from the previ- secondary yolk stage and lower (Fig. 4d, f). ous spawning season were scattered in some Post-ovulatory follicles (Fig. 4f) were found ovaries. The oocytes in the perinucleolus stage in six ovaries, which included four ovaries in occupied a large portion of the ovary with a few fish of <100 mm SL (87.0-95.3 mm SL, GSI = oocytes at the yolk-vesicle stage intermixed 2.6-6.7), and were also found with advanced (87.0-148.3 mm SL, GSI = 1.0- 6.6, n = 10) oocytes, which was the migratory nucleus stage (Fig. 4h). The ovaries in the resting phase were in the most advanced oocytes. The ovaries in defined as being in a state immediately following the maturation phase were defined as being in a the termination of the previous spawning season. state in which it was possible to spawn or very The developmental phases were observed close to spawning, or just after spawning. during summer-spring (August 2012-May 2013, (3) Resting phase: GSI was 0.4-6.6 (n = 67) September 2013-May 2014, and September 2014-March 2015) for the vitellogenic phase, 20 a spring-summer (April-June 2013, and March- 15 July 2014 or 2015) for the maturation phase, 10 and summer-winter (July- October 2012, June 5 2013-January 2014, and June-November 2014) 0

(%) 20 for the resting phase (Fig. 6).

y b 15 10 Ovarian maturity and environmental conditions frequenc 5 Water temperature changed seasonally 0 between 5.0 and 22.8°C (Fig. 7). Day length Relative 20 c varied from 9 h 46 min to 14 h 34 min. The envi- 15 ronmental conditions were 7.5-20.8°C and 9 h 10 47 min-14 h 33 min for the vitellogenic phase, 5 and 10.2-18.5°C and 11 h 55 min-14 h 33 min for 0 200 300 400 500 600 700 800 900 the maturation phase (Fig. 8). Oocyte diameter (µm)

Fig. 5. Relative frequency (%) distribution of oocyte diame- Total fecundity ters in Barbatula oreas. (a) vitellogenic phase (121.0 mm SL, TF was calculated using ovaries in the vitello- GSI 15.0, November 2012, n = 424); (b) vitellogenic phase genic phase, close to spawning, collected from (114.8 mm SL, GSI 15.7, February 2015, n = 321); (c) matu- ration phase (125.8 mm SL, GSI 7.4, June 2013, n = 405). January to March (73.2-149.4 mm SL, n = 34).

100 44234565573555617467511 3765811 656910 5108 6 5555 (%)

50 frequency Relative

0 AM JJASOND JFMAMJ JASOND JFMAMJ JASOND JFMAM JJA 2012 2013 2014 2015 Fig. 6. Monthly changes in relative frequencies (%) of ovarian-developmental phases in Barbatula oreas. , vitellogenic phase; , maturation phase; , resting phase. The Arabic numerals indicate the number of individuals. 128 R. Hatakeyama and T. Kitano

25 16 20 ) C) ˚ (h ( 14

15 th

12 leng 10 y mperature Da Te 5 10

0 8 AM JJASOND JFMAMJ JASOND JFMAMJ JAS OND JFMAMJ JA 2012 2013 2014 2015

Fig. 7. Seasonal changes in daily mean water temperature (solid line) and day length (dashed line) in the Kaname River.

16 TF = 0.0007SL3.3263 (n = 34, r = 0.94).

) 14 Meanwhile, the TF of fish in the Komaoi (h

th River numbered 1,564-2,685 per ovary (86.3- 12

leng 105.3 mm SL, n = 6) (Fig. 9). y

Da 10 Discussion 8 5 10 15 20 25 Temperature (˚C) It was estimated that B. oreas of < 100 mm SL in April were born in the previous year in Fig. 8. Relationship between water temperature and day the Kaname River (Hatakeyama et al. 2017). As length at appearance of ovarian-developmental phases in Barbatula oreas. ×, maturation phase (n = 16); •, resting post-ovulatory follicles were detected in fish of phase (n = 21); ○, vitellogenic phase (n = 27). The dark < 100 mm SL, it is apparent that females spawn and light-shaded areas indicate the range of combinations at age-1. Semina, which likely include sperma- of water temperature and day length, when ovaries are in tozoa, from genital ducts in fish of < 100 mm SL the maturation and vitellogenic phases, respectively. suggest that males may also spawn at age-1. Males produced semen throughout the year, 12000 Kaname River: while females exhibited an obvious annual cycle in 3.3263 10000 TF = 0.0007SL r = 0.94 GSI and ovarian maturity. The ovaries in the matu- 8000 ration phase, at a state of spawning, appeared from March to July. Therefore, B. oreas is believed 6000 to spawn from March to July, with the timing tal fecundity

To 4000 regulated by female maturation. Spawning may

2000 occur mainly in earlier months, as small fish of < 20 mm SL were found only in the first half of 0 60 80 100 120 140 160 the spawning period (Hatakeyama et al. 2017). Standard length (mm) In spring-early summer spawning species, yolk Fig. 9. Relationship between standard length and total globules begin to accumulate from autumn; fecundity in Barbatula oreas. ●, Kaname River (n = 34); ○, October, e.g. in Misgurnus anguillicaudatus Komaoi River (n = 6). (Kimura and Koya 2011), Pseudorasbora pugnax (Ohnaka et al. 2009), and age-1 Gnathopogon Based on the frequency distribution of oocyte caerulescens (Okuzawa et al. 1986), and September, diameter, oocytes of > 600 μm in diameter were e.g. in Micropterus dolomieu (Yambe et al. 2004), defined as advanced yolked oocytes. and age-2 M. salmoides (Yodo and Kimura 2002). TF numbered 1,049-10,671 per ovary (Fig. 9). The earlier initiation in accumulation of yolk glob- The relationship between the TF and SL was ules in B. oreas, which was from August, suggests regressed by power functions as follows: that vitellogenesis progresses under a wider Reproductive biology of Barbatula oreas 129 range of water temperatures (7.5-20.8°C) and/ age-2, and approximately 125 mm SL at age-3. or day lengths (9 h 47 min-14 h 33 min), com- Therefore, total fecundity of B. oreas in the pared with other species. Kaname River is estimated to be approximately Longer days and/or increasing temperatures 1,497 eggs per spawning at age-1, approximately were mentioned as important environmental 4,319 eggs at age-2 and approximately 6,608 eggs factors determining the initiation of spawning at age-3, and the total number of eggs produced periods in spring-early summer spawning spe- during the lifetime is estimated to be 12,424. cies (Shimizu and Hanyu 1983; Asahina et al. 1985; Ota et al. 2015). The monthly mean GSI of Maturation and fertility in a temperate river female B. oreas was already high during winter, The spawning period of B. oreas in the Kaname but the ovaries in the maturation phase did not River was regulated by the female maturation. appear until March (10.2°C, 11 h 55 min). The Vitellogenesis began from August (19.9°C, 13 h closely-related B. barbatulus in Siberia spawns 24 min) and continued until the next spawning not only from April to May, but also from August season, occurring under a wide range of water to October, i.e., under short-day length, in a year temperatures and day lengths (7.5-20.8°C, 9 h in which water temperature is higher (Skryabin 47 min-14 h 33 min). The spawning season 1993). Although the influence of day length is appeared to begin from March (10.2°C, 11 h unclear, B. oreas spawning in the Kaname River 55 min) and continue until July (18.5°C, 14 h seems to occur when there is a transition to a suit- 14 min). These environmental conditions, which able temperature, approximately 10°C in spring. enable ovarian maturity, may exist widely in As at least two oocyte groups existed simul- lower latitudinal rivers in Japan than the Kaname taneously in an ovary, the process of oocyte River. When B. oreas is introduced into such development in B. oreas is categorized as rivers, gonadal maturity is expected to progress. being group-synchronous oocyte development For B. oreas naturally distributed in the (Wallace and Selman 1981; Takano 1989). In subarctic regions, high temperature seems to most species with group-synchronous oocyte influence establishment when introduced in development, total fecundity provides an indi- lower latitudinal regions. However, the upper cation of annual fecundity, the total number of temperature limit for B. oreas survival is not eggs spawned by a female per year, because no clear, though it is doubtless able to withstand up yolked oocytes are not regarded as developed to approximately 23°C, which was the maximum and are not added to the larger oocyte group after temperature in the Kaname River habitat. It is initiation of vitellogenesis in the ovary (Hunter et known that the lower limit of its distributional al. 1992; Kurita 2010). Total fecundity in B. oreas range corresponds with that of Oncorhynchus may also be an indication of annual fecundity. masou, extending to some lower reaches in the The simultaneous appearance of post-ovulatory rivers of Hokkaido (Miyadi et al. 1963). The follicles and advanced oocytes in an ovary implies upper temperature limit at which feeding ceases that this species spawns advanced oocytes or dying-off begins is 26°C in O. masou (Takami dividing into several clutches. However, the two and Sato 1998). Therefore, the high-temperature oocyte groups were not completely separated tolerance limit in B. oreas may be around 26°C. and intermediate diameter oocytes were present Barbatula oreas, distributed naturally in the during the pre-spawning to spawning season, Komaoi River, grow to approximately 55 mm SL although they were few in number. More detailed at age-1, approximately 95 mm SL at age-2 and consideration is needed as to whether small approximately 135 mm SL at age-3 (Hatakeyama oocytes develop and are spawned. et al. 2017), and is presumed to spawn for the According to the growth equation of B. oreas in first time at age-2 (Hatakeyama et al. 2017). The the Kaname River (Hatakeyama et al. 2017), body TF-SL relationship is unknown in B. oreas in the size is calculated to be approximately 80 mm SL Komaoi River, but TF was not greatly different in April at age-1, approximately 110 mm SL at from that in the fish in the Kaname River. When 130 R. Hatakeyama and T. Kitano the relationship was applied to B. oreas in the Conover, D. O. (1992) Seasonality and the scheduling Komaoi River, the total number of eggs produced of life history at different latitudes. Journal of Fish Biology, 41 suppl. B, 161-178. in a lifetime was estimated to be 11,187, in con- Hatakeyama, R., T. Kitano and Y. Machida (2017) Growth trast to 12,424 in the fish in the Kaname River. and early gonadal development in boreal Barbatula Taki and Kanou (2008) expressed the sim- oreas ( Jordan & Fowler, 1903) introduced into a tem- Biogeography plest concept of alien fish invasiveness as perate river in central Honshu, Japan. , 19, 163-171. follows: Invasiveness = Invasive biological char- Hosoya, K. (2013) Family Cobitidae. In “Fishes of Japan acteristics (e.g., habitat characteristics, feeding with Pictorial Keys to the Species. Vol. 1. 3rd edition” habit, fertility) × High introductive opportuni- (ed. by T. Nakabo), Tokai University Press, Tokyo, pp. 328-334 (in Japanese). ties. Fertility is an important parameter deter- Hunter, J. R., B. J. Macewicz, N. Chyan-huei Lo and C. A. mining invasiveness. The potential fecundity Kimbrell (1992) Fecundity, spawning, and maturity of in a lifetime of B. oreas may not differ much female Dover sole Microstomus pacificus, with an eval- between the Kaname River and Komaoi River, uation of assumptions and precision. Fishery Bulletin, U.S., 90, 101-128. however, B. oreas in the Kaname River mature Ikeda, H. (1936) On the sexual dimorphism and the taxonomi- in the short term; that is, they have a high cal status of some Japanese loaches. Zoological Magazine, intrinsic rate of natural increase. 48, 983-994 (in Japanese with English abstract). The life history traits of B. oreas may differ Kimura, A. and Y. Koya (2011) Annual reproductive cycle of a wild population of oriental weather loach depending on the environmental characteristics Misgurnus anguillicaudatus in Gifu Prefecture, central in each river (Villeneuve et al. 2005; Trippel and Japan. Japanese Journal of Ichthyology, 58, 1-12 (in Harvey 2011), but the spawning season may Japanese with English abstract). Kottelat, M. (2012) Conspectus cobitidum: an inventory also be initiated earlier in the lower latitudinal of the loaches of the world (Teleostei: Cypriniformes: rivers, because a thermal rise in spring occurs Cobitoidei). The Raffles Bulletin of Zoology, Suppl. 26, earlier (Lam 1983; Conover 1992; Hatakeyama 1-199. et al. 2017). Thus, it is predicted that the Kurita, Y. (2010) Influence of spatio-temporal changes in stock reproductive potential on the recruitment levels growth period after hatching will be prolonged. of fish. Bulletin of the Japanese Society of Fisheries Additionally, growth is possible during winter Oceanography, Suppl. 74, 4-18 (in Japanese with due to higher temperatures (Hatakeyama et al. English abstract). 2017). Therefore, when this species is introduced Lam, T. J. (1983) Environmental influences on gonadal activity in fish. In “Fish Physiology, Vol. IX” (ed. by in rivers further south than the Kaname River, W. S. Hoar, D. J. Randall and E. M. Donaldson), where the water temperature does not rise above Academic Press, New York, pp. 65-116. a certain level during summer, it is expected that Masuda, H. and Y. Kobayashi (1994) Cobitidae. In “Grand Atlas of Fish Life Modes , Tokai University Press, the SL at first maturation will be larger and the ” Tokyo, pp.40-41 (in Japanese). fertility of the population will increase further. Ministry of Land, Infrastructure, Transport and Tourism (2007) River Environmental Database. Acknowledgements http://mizukoku.nilim.go.jp/ksnkankyo/index.html, accessed on 11 Oct. 2016 (in Japanese). Miyadi, D., H. Kawanabe and N. Mizuno (1963) Barbatula We thank Shinichi Murata, Ryosuke Tanamoto, toni toni (DYBOWSKI). 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本州中部の温帯河川に定着したフクドジョウ Barbatula oreas の繁殖特性

畠山類・北野忠

神奈川県・金目川に定着した北海道原産のフクドジョウ Barbatula oreas について繁殖特性を調べ た。雄では GSI の季節変化が不明瞭で，精液の出る個体が周年認められた。雌では GSI が季節的に 変化し，3 ～ 4 月に高く，7 ～ 8 月に低かった。卵巣の成熟段階は 3 相に分けられ（卵黄蓄積相，成 熟相，休止相），産卵期の特徴を示す成熟相の卵巣は 3 ～ 7 月に認められた。排卵後濾胞は満 1 歳と 推定される体長100 mm 以下の個体でも認められ，孵化の翌年には成熟すると判断された。第一卵群 の卵母細胞数は1,049 ～ 10,671で，体長増加に伴い累乗関数的に増加した。卵巣への卵黄蓄積は幅広 い水温と日長の条件下（7.5 ～ 20.8°C，9 h 47 min ～ 14 h 33 min）で進み，産卵期の開始は産卵適水 温（10.2 ～ 18.5°C）への移行により起こると考えられた。満 1 歳で成熟する本個体群は，自然分布域 の個体群に比較して高い内的自然増加率を持つと考えられた。