From the viewpoint of species conservation and fisheries management, the growth and reproductive ecology of
Sample collection and measurements
In total, 50-100 individuals of
The extracted gonads were fixed with Bouin’s solu-tion, then embedded in paraffin, sectioned at a thickness of 3-5 ㎛, and stained with Mayer’s hematoxylin and 0.5% eo-sin (H&E). Assessment of the developmental stage of the go-nads and their relative stages was based on that of Yasutake and Wales (1983). The gonads were observed under an opti-cal microscope, and gonadal development was classified into five phases: immature, mature, ripe, spent, and degenerated.
Spawning characteristics and early life history
To examine the habitat structure of
was excavated, following the method of Koga and Noda (1992). Egg masses protected by a parent in the spawning bur-row were collected with the aid of fishermen and transferred to the laboratory. Egg diameter and larval size were measured using the Image Pro Plus program (version 4.5; Cybernetics, USA) with a stereomicroscope (SZH10, Olympus, Japan). The shapes of embryos in the eggs and larvae after hatch-ing were observed and photographed using a digital camera attached to the stereomicroscope. The hatched larvae were reared in a small water tank at a water temperature of 20℃ for 5 days. The terminology used for eggs and larvae followed that of Russell (1976) and Okiyama (1988).
[Table 1.] Collection data of Scartelaos gigas from Jung-do Island Korea in 2003
Collection data of Scartelaos gigas from Jung-do Island Korea in 2003
The biweekly variations in the gonodosomatic index (GSI) of
[Fig. 2.] Monthly change in gonadosomatic index (GSI) of Scartelaos gigas. Open circles indicate mean and bars indicate minimum and maximum.
[Fig. 3.] Histological sections showing developmental stages of male Scartelaos gigas.(A) Immature stage 30 April (B) Mature stage 10 June (C) Ripe stage 25 June (D) Just after spent stage 7 July (E) Spent and degenerative stage 21 September. Ps primary spermatocytes; Sd spermatids; Ss secondary spermatocytes; Sl seminiferus lobuli; Sz spermatozoon; Tl testicular lobule.
[Fig. 4.] Histological sections showing developmental stages of female Scartelaos gigas.(A) Immature stage 30 April (B) Mature stage 25 June (C) Ripe stage 10 June (D) Just after spent stage 15 July (E F) Degenerative and resting stage 13 August (E) and 21 September (F). N nucleus; No nucleolus; Oc ovarian cavity; Od oil droplet; Og oogonia; Ol ovarian lamella; Oo oocytes; Po primary oocytes; Yg yolk globule.
hematoxylin, and spermatozoa developed from spermatids were observed in an 18.0-cm TL specimen, collected in June 2003 (Fig. 3B). Spermatocytes, spermatids, and spermato-zoon were observed in a 12.3-cm TL specimen collected in June 2003 (Fig. 3C). We confirmed that mature spermatozoa exit through the testicular tubule and the spermatic duct, as observed in a 14.2-cm TL specimen collected in July 2003. Many sperm were visible in the narrow lumens (Fig. 3D). The number of mature spermatozoa aggregated densely in the testicular cyst was decreased due to release of sperm, and the lobular lumen became too weak to maintain a vacuolar structure. A specimen of 18.4 cm TL collected in September 2003 had thicker epithelial tissue in the testicular tubule (Fig. 3E). These results led us to conclude that the gonadal tissue of male
The female gonads have a saccular shape and are located on the left and right sides of the posterior abdominal cavity. Early oocytes of approximately 50-150 ㎛ in diameter and 1-3 nucleoli were seen in the nucleoplasm of a 18.2-cm TL female specimen collected in April 2003 (Fig 4A). An oocyte of 200-380 ㎛ in diameter and containing a yolk globule and oil droplets only in the cortical layer of the cytoplasm, and mature eggs containing a fused yolk granule and without a visible nucleus were observed in a 13.7-cm TL specimen collected in June 2003 (Fig. 4B). Mature oocytes of 200-400 ㎛ in diameter with a homogeneous appearance were found in a 17.1-cm TL specimen collected in June 2003 (Fig. 4C). Many oil droplets were seen in 150-370 ㎛ oocytes in a 13.7-cm TL specimen collected in July 2003 (Fig. 4D). Oo-cytes and oogonia were seen along with ovarian lamellae in a 16.9-cm TL specimen collected in August 2003 (Fig. 4E). No mature eggs, but 20-30 ㎛ resting early oocytes were observed in a 19.2-cm TL specimen collected in September 2003 (Fig. 4F). These results suggest that the gonadal tissue of female
The mean sex ratio was 53:47 (female:male); in particu-lar, the ratio of males was significantly higher in October (
[Fig. 6.] Habitat cave of Scartelaos gigas. (A) Entrance (B) Real passage (C) Spawning cave (D) Camouflage passage (E) Mud surface. Egg mass of S. gigas was found in the upper layer of spawning cave along with one male protecting egg mass. Sometimes both one male and one female were found in the spawning cave during spawning season. Fishermen obstructed escape of S. gigas by stepping on real passage then catched S. gigas through entrance by hand.
One male specimen was found protecting eggs in the spawn-ing burrow. The spawning burrow was oval and 20-25 cm in length, allowing air to exit the burrow (Fig. 6). The eggs ad-hered to the upper surface of the spawning burrow, attached by numerous fine filaments (Fig. 7A and 7B).
The spawned eggs had an elliptical shape, with a long axis of 1.23-1.48 mm (1.37 ± 0.07 mm,
Hatched larvae had a TL of 2.58-3.24 mm (mean, 3.03;
[Fig. 7.] Eggs and larval development of Scartelaos gigas. (A) Egg mass (B) Embryonic stage (C) Just-hatched larva (D) Three days larva after hatching (E) Five days larva after hatching.
yolk were observed. The oil globule was located in the ante-rior portion of the yolk. There was one melanophore on both the dorsal and ventral portions of the anus and there was one large branch-shaped melanophore on the ventral contour be-tween the 18th and 19th myomeres (Fig. 7B). Three days after hatching, larvae had a TL of 3.05-3.26 mm (mean, 3.17 mm;
Testicular structure in teleosts can be classified into two types: tubular and lobular, depending on the pattern of sper-matogenesis (Billard et al., 1982). The testis of
Teleost ovaries can be divided into three types based on the pattern of oocyte development: synchronous, group synchro-nous, and asynchronous (Nagahama, 1983). Oocyte develop-ment in
The GSI was highest in May for
The elliptical-shaped eggs of
The number of eggs produced is an indicator of species productivity. Studies have found 5,000-20,000
The melanophore is an important characteristic for identifi-cation of species during the larval stage (Russell, 1976; Ken-dall et al., 1984).
Implications for conservation of S. gigas
Ryu et al. (1995) studied the distribution of