Naohiko Takeshita

A note on the reproductive ecology of the catadromous fourspine sculpin,cottus kazika (scorpaeniformes: Cottidae)

T he seven species of tYeshwater sculpins inhabiting the Japanese Archipelago (6 Corers and 1 Trachidermus) exhibit various life history characteristics, such as catadromous, amphidromous, lacustrine and fluvial (Goto, 1990). Both the fourspine sculpin, C. kazika, and roughskin sculpin, 77 jasciatus, have a catadromous life style. The forrner is indigenous to Japan, being found in Honshu, Shikoku and Kyushu Islands. The species migrates from the middle and lower reaches of rivers to the sea tbr spawning in late autumn and winter (Miyadi et al., 1976; Nakamura, 1963). However, little is known about its reproductive ecology, the only available evidence being a collection of egg clusters and attending males taken at the mouth of the Nagara River, where salinity ranged from 16 to 18 ppt (River Bureau, Ministry of Construction and Water Resources Development Public Corporation, t992). This paper reports further aspects of the reproductive ecology of (7. kazika.

Spawning grounds and nests of Trachidermus fasciatus (Cottidae) in the Kashima and Shiota estuaries system facing Ariake Bay, Japan

Abstract The spawning grounds of a cottid fish, Trachidermus fasciatus, were investigated off the mouth of the Kashima River in Ariake Bay from January to March, 1996–1999. The nests were found about 1.1–2.3 km off the mouth of the river, where the bottom salinity was 8‰–21‰ at low tides. Oyster shells were mainly found to be used as nests. A male, a pair, a male and egg clusters, a pair and egg clusters, or a female were found inside shells. The average number of guarded egg clusters per male in shells was 1.3 ± 0.4.

Egg Survival in a Fluvial Population of Masu Salmon in Relation to Intragravel Conditions in Spawning Redds

Abstract Yamame are a fluvial population of masu salmon Oncorhynchus masou (also known as cherry salmon) that typically live in the mountain streams of Kyushu Island, Japan. We estimated the seepage of water through spawning redds by injecting carbon ink into the redds and periodically sampling the intragravel water. We found that the survival of yamame from egg deposition to the eyed stage was strongly dependent on the permeability of the gravel. We estimated permeability during two periods, just after spawning was completed and after eggs had reached the eyed stage. We found reduced permeability from the time of spawning to the time when the eggs reached the eyed stage. These results imply that the permeability of redds is one of the most important factors in the survival of embryos from fertilization to the eyed stage of development.

Embryonic, larval and juvenile development of the roughskin sculpin,Trachidermus fasciatus (Scorpaeniformes: Cottidae)

Embryonic, larval and juvenile development of the catadromous roughskin sculpin,Trachidermus fasciatus, were described using eggs spawned in an aquarium. The eggs, measuring 1.98–2.21 mm in diameter, were light reddish-yellow and had many oil globules, 0.05–0.18 mm in diameter. Hatching occurred 30 days after spawning at 2.3–11.3°C. The newly-hatched larvae, measuring 6.9–7.3 mm BL, had a single oil globule, 9–10+25–26=34–36 myomeres and 6 or 7 large stellate melanophores dorsally along the gut. The yolk was almost resorbed, number of pectoral-fin rays attained 16–17, and two parietal, one nuchal and four preopercular spines were formed, 5 days after hatching, at 8.2–8.4 mm BL. The oil globule disappeared, and one supracleithral spine was formed, 11 days after hatching, at 8.9–9.5 mm BL. Notochord flexion began 15 days after hatching, at 9.7–10.3 mm BL. A posttemporal spine was formed 20 days after hatching, at 10.7–10.9 mm BL. The first dorsal fin spines (VII–VIII), second dorsal fin and anal fin rays (18–19, 16–18, respectively) appeared 23 days after hatching, at 12.0–13.7 mm BL. The pelvic fin spine and rays (I, 4) were formed and black bands on the head and sides of the body began to develop 27 days after hatching, at 13.8–15.8 mm BL.Newly-hatched larvae swam just below the surface in the aquaria. Preflexion larvae (8.9–9.5 mm BL), in which the oil globule had disappeared, swam in the middle layer, while juveniles (13.8–15.8 mm BL) began swimming on the bottom of the aquaria. Swimming behavior observed in the aquaria suggested that the fish started to change to a demersal existence at the juvenile stage.

Growth of the fourspine sculpin Cottus kazika in the Gonokawa River, Japan, and effects of water temperature on growth

The fourspine sculpin Cottus kazika is indigenous to Japan and found in Honshu except for the waters facing the Seto Inland Sea, and was also found in southern Shikoku and eastern Kyushu. This species has a catadromous life style and migrates as juveniles from the sea to the middle reaches of rivers to grow. The growth pattern of this fish was investigated by a mark-and-recapture method from July 1994 to December 1996, in the Nigorikawa River, a tributary of the Gonokawa River system, Shimane Prefecture. 0-year-old fish of 50–70 mm total length (TL) occurred in the study area from June to July, grew to 90–140 mm TL by the following April, and attained 160–210 mm TL by December. This fish grew rapidly in September–November and April–July, almost ceasing to grow in July–September. It seems that this stagnant growth phase in summer is a characteristic of the seasonal growth pattern of C. kazika. A rearing experiment indicated that the growth rate of C. kazika was higher at 16–22°C than at 12–14 and 24–26°C. This result supports the field evidence of a stagnant growth phase in summer in the Nigorikawa River.

Movement of the fluvial form of masu salmon, Oncorhynchus masou masou, in a mountain stream in Kyushu, Japan

Using mark-recapture methods, the movements of the fluvial form of masu salmon (Oncorhynchus masou masou) in a mountain stream on the island of Kyushu, Japan, were studied. Most (78%) of the masu salmon were recaptured in the pool in which they had been originally caught and tagged. Of those that moved between pools, the proportion of individuals that moved during the breeding period was not significantly higher than the proportion that moved during the non-breeding period. However, during the breeding period, a higher proportion of larger salmon moved than did smaller fish. The proportion of mobile large males during breeding period was higher than that for small males. Also, it was found that a few individuals showed long-range movement in the autumn. As a long-term movement, 78 individual fish (65%) that were recaptured more than three times showed high sedentary tendencies. Sixteen individual mobile fish (13%) moved and returned to the original pool. Fluvial form of masu salmon in Kyushu show a high sedentary nature; however, large mature males seem to actively move in search of female during breeding period.

Estimation of the frequency of maturity and sexual differences in the maturation period of the roughskin sculpin Trachidermus fasciatus

In Japan, the catadromous roughskin sculpin Trachidermus fasciatus, belonging to the family Cottidae, is found in Ariake and Isahaya Bays, and in the rivers flowing into these water bodies. Several studies have been published on the reproductive ecology of this fish. However, estimates on the maturation of this species are not available. In this present study, the authors estimated the frequency of maturity stages and sexual differences in the maturation periods of T. fasciatus collected from the Kashima River and Ariake Bay. Specimens were collected 3 km upstream from the mouth of the Kashima River in Kyushu Island, Japan, between November 1994 and January 1995. Until 1995, no specimens have been collected from Ariake Bay because the spawning grounds of this species were unknown. However, in a previous study conducted in 1999, the spawning grounds of this species were found for the first time to be 1.1– 2.3 km away from the mouth of this river. In addition, the individuals caught in May 1997, at approximately 1.5 km upstream the mouth of the Naka River (the tributary of the Kashima River), were used as the specimens in postspawning season. The males and females that were collected in this study were also used as specimens in the present study. In total, 69 (85.3–161.3 mm body length [BL]) female and 60 (82.4–146.7 mm BL) male specimens were collected. These specimens werefixed in10%buffered formalin, and thegonads were removed. The gonad weight (WG; mg) and body weight (WB; mg) were measured, and the GSI (I) was calculated using the following equation: