SUISANZOSHOKU 47(2), 209-214 (1999)

Reproduction of the Japanese , japonica, in Tateyama Bay

SULISTIONO* 1, Seiichi WATANABE* 1, and Masashi YOKOTA* 1

(Accepted March 5, 1999)

Abstract: The maturity stages of gonads and the fecundity of the Japanese whiting, Sillago japonica, were investigated from October 1993 to January 1995 in Tateyama Bay using samples collected by encircling trammel net and hand line. Sex ratio (M/F) of the varied from 0.68 to 1.67. Both male and female had a peak CF (condition factor) value in June (0.86 in female and 0.83 in male). The peak value for GSI (gonad somatic index) was observed in August (4.19 in female and 1.62 in male). The maturing and mature stages of gonads were observed from June to October, whereas the immature gonad was found during November to May. Fecundity of S. japonica varied from 13, 600 to 68, 900. The GSI, CF, gonad maturity stages and size frequency of the ova-diameter indicated that the spawning period of the S. japonica was also quite long.

Key words: Sillago japonica; Reproduction; Tateyama Bay

Japanese whiting, Sillago japonica, is distri- buted in Japan, , and South east Materials and Methods

Asia and is commercially fished in those countries1). They are mostly caught in coastal Sampling was carried out monthly in Tateyama waters using beach seines, gill net and trammel Bay (139•‹49'-139•‹51'E and 34•‹59'-35•‹01'N) using net, but considerable quantities are also taken in an encircling trammel net. The samples were nearshore deeper waters using beam and otter transported to the laboratory and the total length trawl nets1). TL (nearest 1 mm) and body weight BW

Drops in catches of the fish have been attri (nearest 0.01 g) were measured. Gonads were buted to change in the environment and over- dissected, and maturity stages were estimated fishing, and further decreases in the availability (Table 1) using a modified gonad stage classifica- of this family in nature are anticipated. However, tion method2'3) as sillaginids have a great potential for fish cul . Condition factor (CF) was calculated by the ture including in estuarine waters such as within equation CF=105BW/TL3. Gonad Somatic Index brackish water ponds, their offers (GSI) was calculated as GSI=102GW/(BW-GW), distinct economic opportunities in Asia. Sillagi where GW is gonad weight (g). Fecundity was nids, known for their•gdelicious eating•h, are analyzed by using gravimetric methods4). Ova important foodfish at all sizes. diameter was determined to the nearest 0.001

Accordingly, this study was conducted to mm by measuring 100 ova of each fish under a determine some of the unknown biological microscope (40 times enlargement). information of the Japanese whiting in nature such as the maturity stages of the gonads, Results spawning pattern and the fecundity, which is important for further population studies. Sex Ratio and Condition Factor Among the fish we examined, the sex ratio

*' Tokyo university of Fisheries , Dept. of Aquatic Biosciences, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan. 210 Sulistiono, S. watanabe, and M. Yokota

Table 1. Gonad maturity stages of Sillago sp. modified from Palekar and Bal (1961) and Effendie (1979)

Fig. 1. Monthly changes of the sex ratio of the Japanese whiting, Sillago japonica, collected from October 1993 to January 1995 in Tateyama Bay. Monthly sample size was shown at each dot.

Fig. 2. The relationship of the fish size and sex ratio of the (M/F) varied from 0.68 to 1.67 (Fig. 1). The Japanese whiting, Sillago japonica, collected from male outnumbered the female in samples col- October 1993 to January 1995 in Tateyama Bay. Sample size in each class interval was shown at each lected in October 1993, December 1993, March dot. 1994, July 1994, September - October 1994, and January 1995. However, the sex ratio was not October 1993, both female and male showed significant, (X2 test:p=0.41). Correlation between similar value (around 0.8). It decreased to 0.76 sex ratio and total length indicated that the male in November, and then underwent a little outnumbered female in small size (135 mm), increase during December 1993. The similar nevertheless the ratio of female increased in the pattern was also found in the sample collected in larger size (205 mm, 215 and 225 mm) (Fig. 2). January 1994. In February, March and April This relation was significantly different (X 2test: 1994, the condition factor of fish increased, and p =0.012). reached the peak in June. The condition factor The condition factor increased during the was not correlated with total length during a spring and summer, with a peak of 0.86 for spawning season (June - October) (Fig. 4). female and 0.83 for male, and declined during autumn and winter. The seasonal changes in Gonad Maturation Stages and Gonad Somatic condition factor were observed (ANOVA, p< Index (GSI) 0.01) (Fig. 3). In the sample collected during Most fish exhibited gonad maturity stage III Reproduction of Sillagojaponica in Tateyama Bay 211

(maturing) or IV (mature) during May to September. In June, the fish in these categories were 87% in female (stage III 39%, stage IV 48%), and 86% in male (stage III 45%, stage IV 41%). In July, 100% (stage III, 42%; stage IV, 41%) of female and 93% (stage III, 32%; stage IV, 61%) of male were in stage III or IV. The similar condition was found in August. In September, maturing and mature female de- creased, but not so in male. In October, matur- ing female and male decreased (84% in female and 56% in male). While the majority of the fish were either in stages II or stage V after November, the most of them were in stage II in the next April. Percentages of mature male and female in each 10 mm length group were observed in the reproductive season. Thirty three percent of female with total length of 135 mm-144 mm was

Fig. 3. Monthly changes of condition factor on the mature. It was approximately 42% in male. In Japanese whiting, Sillago japonica, from Tateyama the interval of 155 mm -164 mm, the mature Bay. Vertical bars indicate standard deviation. gonad was observed in 58% of female and in 43% of male. The number of mature gonad was also increased to 83% in female and 64% in male for interval size 175 mm -184 mm. In the inter- val 195 mm - 225 mm, 80% to 100% of either sex were in mature condition. The monthly fluctuation of the gonad somatic index of S. japonica was shown in Fig. 5. Peak values of GSI were observed from June to Octo- ber, during which the maximum values for female and male were 4.19 and 1.62 respectively (in August). The GSI of S. japonica varied according to the maturation stages of the gonad, and was not related with total length.

Fecundity and Diameter Number of in maturing and mature female were ranged from 13,600 (TL 150 mm) to 68, 900 (TL 188 mm). The egg number increased with body size (Fig. 6). In the samples collected during June, the fecundity varied from 14, 300 to 40, 200, and from 13, 800 to 44, 700 in July. The number of eggs increased in August (17, 300 to 39, 000) and Fig. 4. Relationship between fish size and condition factor September (18,300 to 68, 900). The fecundity value of the Japanese whiting, Sillago japonica, in observed during October varied from 13, 600 to spawning season. 30, 400. Based on the relationship between the 212 Sulistiono, S. Watanabe, and M. Yokota

Fig. 5. Seasonal changes of the gonad somatic index of the Fig. 7. Histogram of the oocyte diameter of four different Japanese whiting, Sillago japonica, collected from maturation stages in the Japanese whiting, Sillago Tateyama Bay. Vertical bars indicate standard japonica. deviation.

Egg diameter ranged from 63 m to 563 m

with respect to the maturity stages. Peak of the

egg size distribution occurred at 143ƒÊm in pre- mature fish. Two peaks were observed at

163ƒÊm and 463ƒÊm in maturing, and at 213ƒÊm

and 563ƒÊm in mature stage, respectively (Fig.

7). The data showed multiple spawning.

Discussion

Although the number of female and male showed seasonal fluctuation, the sex ratio was not varied significantly. It was observed that the sex ratio depends on the fish size. Male outnum- bered female in the smaller sized (150 mm) group, but in large sized samples (190 mm), the count of female exceeded that of male (Fig. 2). A similar case was reported in Liza subviridis Fig. 6. Relationship between total length and fecundity of where male outnumbered female in small sized the Japanese whiting, Sillago japonica, in the spawning season (June-October 1994) in Tateyama specimens (20 cm), but in large ones it is Bay. not known the mechanism reason of this phenomenon5). total length and the fecundity, the following Seasonal trends on the condition factor of equations were determined: F0. 0048L3.096, S. japonica may be linked with gonad develop- where F is fecundity and L is total length (mm). ment which increased during spawning season Reproduction of Sillagojaponica in Tateyama Bay 213

and decreased in resting period. In the sampling around 81, 700 eggs every two females13) carried out in December 1993, the CF seemed . In mature fish, the major peak of egg increased, which was not caused by diameter distribution appears at 363 ƒÊm, and a development of the gonad. It is suggested that minor one at 513ƒÊm. This is similar to it this phenomenon was caused by occasional observed in S. japonica from the Seto Inland fullness of the stomach contents. This study can Sea9) (350ƒÊ m and 650 ƒÊm), and S. sihama from not estimate a first maturity size using FC, India2) (100 ƒÊ m and 400ƒÊm). In the present because there was no relationship between fish study, the first maturing fish was 140 mm size and condition factor. The first spawning of TL which corresponded to the 2 year old

S. sihama in India was estimated around 130 group. In S. japonica from Japanese waters, the mm by observing a condition factor6). maturation was also observed in 2 years olds

The spawning season in Tateyama Bay was during the spawning season9~. estimated from June to October from the analysis of the gonad maturation stages and GSI. References The mature and spent were occurred 1) McKay, R. J. (1992): FAO Catalogue, Vol.14 from July to October. This is longer than S. Sillaginid Fishes of the World, FAO, Rome, pp. 87. 2) Palekar, V. C. and D. V. Bal (1961): Studies on the japonica * 2 in Kyushu8. The spawning season of maturation and spawning of the Indian whiting Sillago S. japonica from Japan was mainly in summer. sihama, Forsskal from Karwar waters, Proc. Indian The gonad of S. japonica * 2 begin to develop Acad. Sci., 54B, 76-93. around June and continue to develope until 3) Effendie, M. I. (1979): Metode Biologi Perikanan, around August in Hiroshima with a peak in Yayasan Dewi Sri, Bogor, pp. 112. 4) Cai iet, G. M., M. S. Love, and A. W. Ebeling (1986): July9'. In the S. parvisquamis observed in North Fishes. A field and laboratory manual on their eastern Kyushu, the gonad weight increased structure, identification and natural history. from May to August, with a peak value in Wadsworth, Belmont, pp. 194. 5) Silva, E.I.L. and S. S. De Silva (1981): Aspects of June10). It was found that the S. japonica has the of grey mullets, Mugil cephalus L., adult spawning season from June to September with a populations of a coastal lagoon in Srilangka, J. Fish peak around July in Chikuzen Sea11). The Biol., 19, 1-10. spawning period was a little longer than previous 6) Radhakrishnan, N. (1957): A contribution to the observations (from June to October with a peak biology of Indian whiting-Sillago sihama, Forskal, Indian J. Fish., 4, 254-283. around August) in Tateyama Bay. Taken 7) Sano, M. and K. Mochizuki (1984): A revision of the together the peak of spawning season of Japanese sillaginid fishes, Japan J. Ichthyol., 31(2), Sillaginid fishes, which was around June (S. 136-149. 8) Mio, S. (1965): The determination of the age and parvisquamis) and July (S. japonica) in Hiroshima growth of Sillago sihama Forsskal, Bull. Japan Sea and Kyushu, but around August (S. japonica) Reg. Fish. Lab., 14, 1-18. in northern part Japan, seems relate with 9) Kakuda, S. (1970): Studies on the ecology and fishing temperature. stock of Sillago sihama (Forsskal) through the analysis The equation F=0.0048L3.096was determined of its bottom drift-net fishery, J. Fac. of Fish. Ani. Hus., Hiroshima Univ., 9, 11-55. to show the relationship of total length and 10) Imoto, H., N. Yoshioka, C. Kitajima, and S. Matsui fecundity in mature S. japonica from Tateyama (1997): The age and growth of blue whiting, Sillago Bay. The fecundity of the current study ranged parvisquamis distributed in the coastal waters of from 13, 600 to 68, 900, which was close to that Northern Eastern Kyushu. Nippon Suisan gakkaishi, 63(6), 892-898. of S. japonica from the Seto Inland Sea 20, 000 11) Ito, M. and H. Uchida (1990): Age and growth to 80,0009), and S. sihama from India 14, 0002). of Shirogisu in Chikuzen Sea. Seikaiku Block It was also consistent with previous observations Gyoruikenkyukaihou, 7, 39-44. of S. japonica spawned every day (65-69 times) 12) Kumai, H. and M. Nakamura (1977): On the natural spawning of sand borer, Sillago sihama (Forsskal), around 1,000 to 59, 000 eggs per female12), and Mem. Fac. Agric. Kinki Univ., (10), 39-43.

* 2 As S . sihama were collected outside the known distribution of this species7), they were probably S. japonica. 214 Sulistiono, S. Watanabe, and M. Yokota

13) Kumai, H. and M. Nakamura (1978): Spawning of the laboratory. Bull. Japan. Soc. Sci. Fish., 44(9), 1055. silver whiting Sillago sihama (Forsskal) cultivated in

館 山 湾 に お け る シ ロ ギ ス,Sillago japonicaの 繁 殖

SULISTIONO・ 渡 邊 精 一 ・横 田 賢 史

館 山 湾 に お い て1993年10月 か ら1995年1月 に か け て 漕 ぎ刺 網 に よ り採 集 し た シ ロ ギ ス の 性 比,生 殖

腺 の 熟 度 お よ び 抱 卵 数 を 調 査 し た 。 標 本 の 性 比(雄/雌)は0.68～1.67で あ っ た 。 肥 満 度(CF=BW× 105/TL3)は 雌 雄 と も に6月 が 最 大 で あ っ た(雌:0.86,雄:0.83)。 生 殖 腺 熟 度 指 数(GSI=GW×

102/(BW-GW))は8月 が 最 大 で あ っ た(雌:4.19,雄:1.62)。 生 殖 腺 が 成 熟 ス テ ー ジ3,4に あ る

標 本 は6月 か ら10月,成 熟 ス テ ー ジ1に あ る 標 本 は11月 か ら5月 に 見 ら れ た 。 抱 卵 数 は13,600～ 69,900で あ っ た 。 こ れ ら の 結 果 か ら,館 山 湾 に お い て も シ ロ ギ ス の 産 卵 時 期 は 長 い と 考 え ら れ る 。