FISHERIES SCIENCE 2000; 66: 901–907

Original Article

Relationships between the spot patterns on the head of the Japanese Char Salvelinus leucomaenis, distributed in the Chugoku Region, and water quality

Koichiro KAWAI,1,* Aya MASUHARA2 AND Hiromichi IMABAYASHI1

1Faculty of Applied Biological Science, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8528 and 2Max Value, Age, Mie 514-2200,

SUMMARY: Head spots of chars were examined for 17 rivers of the Chugoku Region, and rela- tionships between the patterns and water quality were analyzed. To enable quantitative comparison, two spot indices, index I, a ratio of the length to the width for the longest spot, and index II, a ratio of the width of the widest spot to the interorbital width, were calculated. Both spot indices were divided into three ranges, and all char specimens were categorized into eight types, from A to H. Type A with short and wide spots was the most dominant in the Nishiki, Gono and Hii Rivers in the central part of the Chugoku Mountain Chains whereas type H with long and narrow spots was the most domi- nant in the Gamo River in the eastern part. Electrical conductivity of the water showed a significant positive relationship to index I whereas it showed a significant negative relationship to index II. In contrast, Fe2+ concentration of the water showed a significant negative relationship to index I whereas it showed a significant positive relationship to index II.

KEY WORDS: char, Gogi, head spot, Nikko-iwana, Salvelinus leucomaenis, water quality.

INTRODUCTION ships between the spot patterns and water quality were examined. In the Chugoku Mountain Chains, fish with the Japan- ese name of ‘Gogi’ (genus Salvelinus), are distributed. However, the criteria for identification of Gogi are MATERIALS AND METHODS equivocal and its taxonomical status is controversial.1–7 Sato8 has reviewed the morphology, ecology and distri- Survey area bution of Gogi in Hiroshima Prefecture. Katayama and Fujioka9,10 have studied the distribution of Gogi in Yam- Twelve rivers flowing into the Japan Sea and five rivers aguchi Prefecture. Takeshita11 has studied the distribu- flowing into the Seto Inland Sea, all originating from the tion of chars in 24 rivers of the Chugoku Region. Chugoku Mountain Chains, were surveyed (Fig. 1). However, no studies have been conducted on the rela- tionships between the morphological characteristics of Sampling methods chars and environmental factors. In this study, chars distributed in the Chugoku Moun- Sampling of chars was carried out by angling, usually tain Chains, comprising two subspecies, S. leucomaenis using earthworms as bait, in the most upper reaches as pluvius (Japanese name, Nikko-iwana) and S. l. imbrius 12 possible for each river in order to collect native fish only. (Gogi), according to Hosoya, were collected from Char samples collected were transported live to the lab- 17 rivers and compared on the shape and size of the oratory using a portable aeration system. head spots among the rivers. Furthermore, relation-

Morphological measurements *Corresponding author: Tel: 0824-247894. Fax: 0824-227059. Email: [email protected] Char samples were photographed from the dorsal view in Received 6 December 1999. Accepted 22 May 2000. the transparent acryl container and measured for total 902 FISHERIES SCIENCE K Kawai et al.

Fig. 1 Map of the Chugoku Region, showing 52 collection sites for char and water samples distributed in 17 rivers. length, body length (to nearest 1.0 mm) and bodyweight (to 0.1 g). Each spot on the dorsal surface of the head was measured for length (to 1.0 mm) and width (to 1 mm) from the photograph. To enable quantitative comparison, two indices were calculated: the spot index I, a ratio of the length to the width of the longest spot; and spot index II, a ratio of the width of the widest spot to the interorbital width (Fig. 2).

Examinations of water quality

A surface water sample was collected at each river. Water samples were examined for Fe2+ concentration by the Fig. 2 Measured head parts of char and calculation methods ammonium thiocyanate method. Electric conductivity of two head spot indices. was measured with a salinometer (YSI model 33; Yellow Springs Instrument Co., Inc., OH, USA) at 20°C.

RESULTS samples collected from each river was usually less than 10, but a relatively large number of samples could be col- Morphological data of char samples lected from the and . The total length, body length and bodyweight were in the ranges Table 1 shows some morphological data of a total of 118 of 68–330 mm, 58–290 mm and 2.9–299.0 g, respectively. char samples collected from 17 rivers. The number of The two spot indices were both highly variable and in Relationships between head spots of char and water quality 903

Table1 Ranges (means) of body sizes and two head spot indices of char collected from 17 rivers River No. of indiv. Total length Body length Bodyweight Spot Spot (cm) (cm) (g) Index I Index II Saba 3 9.2–13.5 7.0–11.0 16.5–39.6 4.5–12.0 0.15–0.20 (11.6) (9.0) (25.1) (7.9) (0.18) Nishiki 6 13.5–18.0 11.5–15.0 22.4–58.5 2.9–8.9 0.17–0.27 (15.6) (13.1) (35.1) (4.4) (0.23) Ohta 6 11.8–22.0 9.8–18.0 13.2–89.4 2.5–6.7 0.14–0.21 (15.6) (12.9) (37.7) (4.2) (0.17) Yoshii 2 15.0–18.5 12.3–15.0 24.1–54.5 2.3–6.2 0.11–0.14 (16.8) (13.7) (39.3) (4.2) (0.12) Chigusa 2 15.0–16.5 12.5–13.0 27.7–42.0 3.6–5.0 0.12–0.16 (15.8) (12.8) (34.9) (4.3) (0.14) Takatsu 10 12.0–18.1 10.3–15.5 15.6–48.9 2.1–6.9 0.13–0.22 (14.9) (12.5) (29.1) (4.3) (0.17) Misumi 1 16.0 14.0 42.1 3.9 0.19 Gono 13 12.5–22.0 10.5–17.8 15.6–107.0 1.4–7.6 0.13–0.26 (17.4) (14.5) (47.0) (3.7) (0.21) Kando 3 17.3–22.5 14.7–17.2 44.9–84.5 2.6–5.6 0.16–0.18 (19.2) (15.7) (58.3) (4.1) (0.17) Hii 8 12.5–22.0 10.5–19.0 14.7–86.4 2.5–6.4 0.15–0.26 (16.7) (13.8) (41.8) (3.5) (0.20) Hino 22 11.8–25.0 9.5–20.3 12.8–126.8 3.2–11.0 0.08–0.23 (17.1) (13.9) (45.1) (5.3) (0.15) Katsuta 2 19.5–23.5 17.0–20.5 63.9–132.7 2.3–3.7 0.17 (21.5) (18.9) (98.3) (3.0) (0.17) Tenjin 4 14.5–20.3 12.0–17.3 24.1–70.1 5.1–10.0 0.11–0.16 (16.7) (14.1) (40.6) (6.5) (0.13) Sendai 28 6.8–33.0 5.8–29.0 2.9–299.0 2.7–12.1 0.07–0.21 (16.8) (14.1) (48.8) (6.0) (0.14) Gamo 3 14.0–18.0 11.0–14.5 19.7–49.3 9.8 0.10–0.13 (15.3) (12.2) (30.6) * (0.12) Yata 3 15.5–18.3 12.7–16.2 27.9–53.7 3.8–9.7 0.10–0.16 (17.3) (15.0) (43.8) (7.3) (0.13) Maruyama 2 15.5–16.0 12.0–13.5 28.3–37.3 7.4–8.1 0.13–0.14 (15.8) (12.8) (32.8) (7.8) (0.14)

* The mean value was not calculated because the index was measured only for one specimen due to the bad condition of the other two specimens.

the ranges of 1.4–12.1 and 0.07–0.27 for indices I and II, long and moderately wide) and H (high index I and low respectively. index II, long and narrow) (Fig. 3). Dominant spot types were examined for each river. A type whose number of specimens (n) for the river was in Dominant spot types the following range was regarded as dominant: nmax/2 < n £ nmax, where nmax is the number of specimens of the most Three ranges were set for each spot index so that the dif- abundant type in the river. Type A was the most domi- ference between the maximal and minimal values were nant for the Nishiki, Gono and Hii River, although type divided into equal parts. All char samples were catego- B, and types B and D were co-dominant for the Hii and rized into eight types: A (low index I and high index II, Gono River, respectively (Fig. 4). Type B was the most short and wide), B (low index I and middle index II, dominant for the Saba, Ota, Takatsu, Misumi, Kando, short and moderately wide), C (low index I and low Hino and Katsuta River, although types E and G, types index II, short and narrow), D (middle index I and high A and E, and types F and C were co-dominant for the index II, moderately long and wide), E (middle index I Saba, Takatsu and Hino River, respectively. Type C was and middle index II, moderately long and moderately the most dominant for the Yoshii, Chigusa, Sendai and wide), F (middle index I and low index II, moderately Yata River, although type E, and types E and H were co- long and narrow), G (high index I and middle index II, dominant for the Chigusa and Sendai River, and the Yata 904 FISHERIES SCIENCE K Kawai et al.

River, respectively. Types E and F were co-dominant for the . Types F and H were the most dom- inant for the Tenjin and Gamo River, respectively.

Water quality

Water samples were collected at a total of 52 sites in 17 rivers (Table 2). Electrical conductivity was variable and in the range of 19–89 mmhos/cm. The Fe2+ concentration was also variable and in the range of 0.003–0.03 mg/L.

Relationships between water quality and spot indices

Electrical conductivity showed a significant positive relationship to index I whereas it showed a significant negative relationship to index II (Fig. 5). In contrast, Fe2+ concentration showed a significant negative relationship to index I whereas it showed a sig- Fig. 3 Eight types of head spots based on two indices. nificant positive relationship to index II (Fig. 6).

Fig. 4 Dominant head spot types for 17 rivers. Dominant types were shown in order of dominance for each river. Relationships between head spots of char and water quality 905

Table2 Ranges (means) of electrical conductivity and Fe2+ One possible explanation for this phenomenon is that in concentration of water collected from 17 rivers the central part of the Chugoku Mountain Chains, rivers River No. of Conductivity Fe2+ often originate from relatively shallow valleys with only sampling sites (mmhos/cm) (mg/L) loose slopes due to their peneplain nature. Thus, where Fe2+ concentration of the water is at a high level a large Saba 1 68 0.008 amount of iron hydroxide sediment (of reddish brown Nishiki 3 26–61 0.005–0.012 hue) from the predominantly granitic soil has deposited (39) (0.009) 13 Ohta 3 24–28 0.006–0.007 on the bottom of creek-type streams. The riverbed dis- (26) (0.006) plays a bright reddish-brown background spread with Yoshii 1 20 0.019 whitish stones, cobbles or gravels. In such environments, Chigusa 1 19 0.005 a char of type A with conspicuous, short and wide (i.e. Takatsu 5 28–55 0.005–0.022 white gravel-like) head spots could have established a (39) (0.010) high fitness by virtue of an effective camouflage to some Misumi 1 88 0.008 predators, such as wild birds or mammals. In contrast, a Gono 6 25–73 0.009–0.025 char of type C, F or H with inconspicuous, short to long (40) (0.014) and narrow (i.e. only faint) head spots may have been Kando 2 31–40 0.012–0.013 easily discovered by and be a victim of the predators due (36) (0.013) to a high contrast of the dark body to the bright back- Hii 6 26–49 0.010–0.027 (35) (0.016) ground of the riverbottom. This hypothesis could be sup- Hino 7 30–89 0.007–0.030 ported by the distributions of type A or type D-like char (51) (0.013) in the rivers originating from the Abukuma Mountain Katsuta 1 22 0.015 Chains14 which also have a peneplain structure, and of Tenjin 1 32 0.005 ‘Amemasu’ (S. l. leucomaenis), possessing large whitish Sendai 11 25–72 0.003–0.015 spots like type A in sinuous flowing lower reaches of the (39) (0.009) rivers in the Region.15 Gamo 1 40 0.015 Electrical conductivity is considered a clear indicator Yata 1 46 0.005 of the trophic status of water because it represents the Maruyama 1 58 0.015 concentration of electrolytes such as nutritional salts - 3- (e.g. NO3 and PO4 ) in the water. It showed a signifi- cant positive relationship to index I whereas it showed a significant negative relationship to index II. That is, the DISCUSSION more eutrophicated the water, the longer and the nar- rower the head spots. This result means that type A char In this study, char samples collected from 17 rivers origi- had adapted to extremely oligotrophic waters. This can nating from the Chugoku Mountain Chains, were cate- be explained by the fact that the unpolluted head waters gorized into eight types (type A to H) on the basis of of a river is likely to flow through peneplain-like topog- head spot patterns using two spot indices. It is not clear raphy in the Chugoku Mountain Chains. Thus, an adap- which types correspond to Gogi or Nikko-iwana because tation to a peneplain-like environment may also have the possession of conspicuous worm-eaten spots on the required an adaptation to extremely oligotrophic waters. head, reaching up to the tip of the snout, is only a dis- However, some direct causalities between electrical con- tinctive character between these subspecies.12 However, ductivity and head spot types (e.g. the effect of electri- applying the description by Miyadi et al.4 which states cal conductivity on shape of spots through water that Gogi possesses white spots as large as or larger than transparency) could not be excluded. a pupil in diameter which extend from the side of the Sizes of specimens used in this study had wide ranges body even to the top of the head and that Nikko-iwana with respect both to body length and bodyweight due occasionally possesses small spots on the head, it would to the paucity in natural stocks of chars in the Chugoku appear that types A and D may correspond to Gogi, and Region. On the other hand, there are no apparent studies types C, F and H to Nikko-iwana. Consequently, types that support a constancy of relative developments of size B, E and G may represent the intermediate morph. and shape of head spots to body size among develop- In this study, type A with short and wide head spots mental stages of char. Therefore, a possibility cannot be proved to be the most dominant in the Nishiki, Gono excluded that both spot indices in this study are only a and Hii rivers in the central part of the Chugoku Moun- function of body size. However, this possibility may be tain Chains. The Fe2+ concentration in the water showed excluded by an observation that specimens of Gogi of a significant negative relationship to index I whereas it immature size have extremely conspicuous and large oval showed a significant positive relationship to index II. spots whereas those of Nikko-iwana of the same size have That is, head spots of chars were inclined to become rather faint and narrow worm-eaten spots (Nishimura F, shorter and wider with an increase of Fe2+ concentration. pers. comm.). 906 FISHERIES SCIENCE K Kawai et al.

Fig. 5 Relationship between electrical conductivity and (a) head spot index I (y = 0.049x + 3.124, r = 0.339, n = 111, P < 0.001) and (b) head spot index II (y = 0.000727x + 0.192, r =-0.272, n = 118, P < 0.01).

Fig. 6 Relationship between Fe2+ concentration and (a) head spot index I (y =-116x + 6.285, r =-0.246, n = 111, P < 0.01) and (b) head spot index II (y = 1.775x + 0.143, r = 0.218, n = 118, P < 0.05). Relationships between head spots of char and water quality 907

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