Batch Fecundity of the Japanese Silver-Biddy Gerres Equulus in the Yatsushiro Sea, Western Kyushu, Japan
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Aquaculture Sci. 56（3），409－413（2008） Batch Fecundity of the Japanese Silver-biddy Gerres equulus in the Yatsushiro Sea, Western Kyushu, Japan 1 2, ＊ 2 2 Khan M. IQBAL , Hiroshi SUZUKI , Jun OHTOMI and Yasuji MASUDA Abstract: The Japanese silver-biddy Gerres equulus (Temminck and Schlegel) is one of the most common shore fishes in the costal waters of southern Japan and commercially important for the local fishery. The batch fecundity of G. equulus was examined from the specimens collected in the Yatsushiro Sea, western Kyushu, Japan in June-September, 2001 and 2002. Batch fecundity (BF) ranged from 15,083 to 92,356. The regression correlation between BF and standard length (SL) for the early and the late spawning period was significantly different and these regressions were expressed as BF＝1.00×10－4 SL3.79 (early spawning period) and BF＝1.30×10－4 SL3.33 (late spawning period), respectively. The BF of females at age 2-10 years was higher in the early spawning period than in the late spawning period. Key words: Gerres equulus; Japanese silver-biddy; Batch fecundity; Yatsushiro Sea Fishes belonging to the family Gerreidae the histological studies suggested that the spawn- are widely distributed in the tropical and sub- ing season of G. equulus continued from June to tropical waters in many parts of the world and September (Iqbal et al. 2007). According to Iqbal typically spawn throughout the year, with one or et al (2007), female G. equulus attained sexual more spawning peak periods (Araujo and Santos maturity at a minimum size of 141 mm standard 1999; Cyrus and Blaber 1984; Sarre et al. 1997). length (SL) and the simultaneous presence of Japanese silver-biddy G. equulus is one of the postovulatory follicles and yolk globules in some most common shore fishes in the costal waters ovaries indicated that this species is a multiple (Usuki 1976). This species is also commercially spawner (Vlaming 1983; Massuti and Morales-Nin important for local fisheries in southern Japan 1997; Moreno et al. 2005). and is fished mainly by gill nets (Iqbal et al. 2006). Some biological studies have been conducted G. equulus is distributed from southern Korea on several species of the family Gerreidae for and southern Japan, except the Ryukyu Islands, developing effective ecological measures due to just north of Sado Island, Niigata, the Sea of to its importance in the fishery. Rao (1968), Japan, and Boso Peninsula, Chiba, the Pacific Cyrus and Blaber (1982, 1983a, 1983b, 1984), Coast of Honshu Island (Iwatsuki et al. 1999; Comparan and Hammann (1989), Badrudeen Nakabo 2000). G. equulus was synonymized with and Pillai (1996) and Horinouchi and Sano G. oyena due to the similarity in their body shapes, (2000) observed the food and feeding or the but differs with regards to several meristic char- feeding mechanism on some Gerres fishes in acters and body proportions (Iwatsuki et al. the different region of the world. Usuki (1976) 1999; Miyanohara et al. 1999). Monthly changes examined the territorial behaviour of G. equu- in the gonadosomatic index and the sequential lus in the vicinity of Seto. Kinoshita (1984) development of the ovaries observed through described the early life history of G. equulus. Received March 22, 2007: Accepted July 15, 2008. 1 United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima 890-0065, Japan. 2 Department of Aquatic Resource Sciences, Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan. ＊Corresponding author. Tel.: +81-99-286-4143; fax: +81-99-286-4133. E-mail: [email protected] 410 K. M. Iqbal, H. Suzuki, J. Ohtomi and Y. Masuda El-Agamy (1988) examined the age and growth taxonomic groups in both temperate and tropi- of G. oyena and Grandcourt et al. (2006) inves- cal region produce eggs in this manner. In the tigated the fisheries biology of G. longirostris present study, we investigated the batch fecun- in the waters of the Arabian Gulf. Kanak and dity as a first step in quantitative analysis at the Tachihara (2006a, 2006b) reported the age and early and late spawning period of this species in growth of G. oyena and Gerres sp. on Okinawa the Yatsushiro Sea, western Kyushu, Japan. Island, Japan. And Iqbal et al. (2006, 2007) stud- ied the age, growth and reproductive biology of Materials and Methods G. equulus in western Kyushu, Japan. However, until now there has been no information about To determine the batch fecundity (BF) of G. the batch fecundity of G. equulus. equulus the samples were collected monthly The batch fecundity is an important factor from the commercial fishing boats in the which should be concerned for the stock man- Yatsushiro Sea, western Kyushu, Japan in agement. Accurate estimation of fecundity are June-September, 2001 and 2002, correspond- important in describing the dynamics of fish ing to the spawning season of this species in populations and in some fishes, all eggs mature these waters (Iqbal et al. 2007) (Fig. 1). These synchronously and are shed in a single batch specimens were caught by gill nets in the early over a relatively brief period of time each year morning hours of the day and brought to the (Conover, 1985). In many fishes, ova mature in laboratory fresh and on ice. Standard length multiple batches that are spawned successively (SL) and body weight (BW) were recorded within one spawning season. These species from the specimens to the nearest 1 mm and have been termed multiple spawners, batch to the nearest 0.01 g, respectively. The gonads spawners, serial spawners or fractional spawn- were dissected from the fish and weighed to the ers by various authors (Bagenal and Braum nearest 0.01 g (GW) while the sex was deter- 1971; DeMartini and Fountain 1981; Gale 1983). mined visually. The ovaries were preserved in Little is known about the patterns in batch 10% formalin for histological determination and fecundity of multiple spawners, even though estimation of batch fecundity. many marine and fresh water fishes from divers Based on the histological observation (Iqbal Japan Fig. 1. Sampling site of Gerres equulus in the Yatsushiro Sea, western Kyushu, Japan. Batch Fecundity of Gerres equulus 411 et al. 2007), females having oocytes in the ter- The regression lines on relationship between tiary yolk globule to the migratory nucleus BF and SL were not significantly different stages (－＞250μm in diameter) were consid- between 2001 and 2002 samples (ANCOVA, p＜ ered as mature fish. Consequently, a total of 81 0.05). The data were thus treated combined for mature females was used to estimate the batch both the years and positive correlations were fecundity. The oocytes－ ＞250μm in diameter found between BF and SL. The correlation was were distributed randomly within the ovary. expressed by the following equation: BF＝6.29 Thus, sub-samples were taken from the middle ×10－4 SL3.48 (n＝81, r 2＝0.702). part of the ovaries (Goncalves and Erzini 2000; Regression lines between BF and SL for the Macchi et al. 2002). early spawning period (June－July) and late BF was estimated using the following for- spawning period (August-September) were sig- mula: BF＝N×W, where N is the number of nificantly different (ANCOVA, p＞0.05) (Fig. oocytes at the tertiary yolk globule-migratory 2) and these regressions were expressed as a) －4 3.79 nucleus stages (－＞250μm) per unit gonad early spawning period, BF＝1.00×10 SL weight (g－1) in pre-weighed (to nearest 0.01 g) (n＝32, r 2＝0.816), b) late spawning period, BF sub-sample, and W is the total weight of ovaries ＝1.30×10－4 SL3.33 (n＝49, r 2＝0.778). in grams. Oocytes larger than 250μm were The average BF at the early spawning period counted under a profile projector (Nikon, ranged from 13,617 to 104,355, whereas at the Tokyo, Japan) using a counting grid. The rela- late spawning period ranged from 13,122 to tionship between BF and SL was expressed by a 68,797 between 2 and 10 year old fish. The aver- power function. The average BF for each age age BF for each age class revealed that during class at early spawning period and late spawn- the early spawning period any age class of G. ing period of G. equulus was calculated from the equulus released more eggs than in the late SL range in each class estimated using the von spawning period at a single spawning (Fig. 3). Bertalanffy growth equation (Iqbal et al. 2006). Iqbal et al. (2007) examined that during the spawning season (June to September), the Results and Discussion ovaries of G. equulus contained yolk globule oocytes and hydrated oocytes of different sizes. Estimated batch fecundity (BF) ranged from Some of the yolk globules were found together 15,083 (141 mm SL) to 92,356 (217 mm SL). with postovulatory follicles in the ovary during 100000 BF 1.00 10－4 SL3.79 80000 ＝ × r 2 = 0.816 n = 32 60000 40000 BF＝1.30×10－4 SL3.33 r 2 = 0.778 20000 n = 49 Batch fecundity (no. of eggs) 0 120 140 160 180 200 220 240 Standard length (mm) Fig. 2. Relationship between standard length (SL) (mm) and batch fecundity (no. of eggs) (BF) for Gerres equulus in the Yatsushiro Sea. Solid and open circles indicate early spawning period (June-July) and late spawning period (August- September), respectively. 412 K. M. Iqbal, H. Suzuki, J. Ohtomi and Y. Masuda 120000 100000 80000 60000 40000 20000 Batch fecundity (no. of eggs) 0 13579246810 Age (years) Fig. 3. Average batch fecundity for each age year calculated for Gerres equulus in the Yatsushiro Sea by spawning period.