Seiichi Matsui

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.

Early development of laboratory-reared redlip mullet, Liza haematocheila

Abstract Eggs and sperm of Liza haematocheila were obtained from mature adults under natural conditions, fertilized artificially and incubated in the laboratory. Larvae and juveniles were reared for about 3 months by feeding with rotifers, Artemia nauplii and artificial feed. Early development and growth were described from a series of live specimens of larvae and juveniles. Fertilized eggs hatched after 80–95 h incubation at 15.6–21.2 °C. Feeding began on the 6th day after hatching, when some yolk still remained. Absorption of the oil globule was completed on the 13th day. The notochord staned to flex on the 15th day. The morphological transition from the larval to the juvenile stage occurred during the 25th to 29th days between 12.0 and 14.0 mm in total length (TL). When the larvae transformed to juveniles, the third anal fin ray had not yet transformed into a spine. The formation of the third anal spine occurred during the 40th to 76th days, between 21.6 and 45.5 mm TL; during this period juveniles transformed to young adults. Changes in proportion of the body parts to total length were observed at approximately 13 mm and 30 mm TL, corresponding to the transformations from larva to juvenile and from juvenile to adult, respectively.

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.

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:

Development of eggs, larvae and juveniles of laboratory-reared blue whiting,Sillago parvisquamis (Percoidei: Sillaginidae)

The embryonic, larval and juvenile development of blue whiting,Sillago parvisquamis Gill, are described from a series of laboratory-reared specimens. Mean egg diameter and mean total length (TL) of newly-hatched larvae were 0.71 mm and 1.58 mm, respectively. The eggs were non-adhesive, buoyant and spherical with an oil globule (mean diameter 0.18 mm). Hatching occurred about 20 hours after fertilization at a temperature of 24.0–25.0°C, newly-hatched larvae having 38–40 myomeres. The yolk and oil globule were completely absorbed 3 days after hatching at 2.8–3.2 (mean 3.0) mm TL. Notochord flexion was completed by 7.2–8.2 (7.7) mm TL, and pectoral and caudal fin rays fully developed by approximately 10 mm and 8.5 mm TL, respectively. Completion of fin development occurred in the following sequence: caudal, pectoral, anal and second dorsal, first dorsal and pelvic, the last-mentioned by approximately 11 mm TL. The larvae ofS. parvisquamis andS. japonica, which closely resemble each other in general morphology and pigmentation, could be distinguished as follows. Newly-hatchedS. parvisquamis larvae had more myomeres thanS. japonica (38–40 vs. 32–34) and more melanophores on the dorsal surface of the body (19–28 vs. about 40).Sillago japonica had a vertical band of melanophores on the caudal peduncle, which was lacking in postflexionS. parvisquamis larvae. In addition, juveniles ofS. parvisquamis (larger than 23 mm TL) had melanophores on the body extending anteriorly to below the lateral line to form a midlateral band, whereas no obvious band occurred on similarly-sizedS. japonica juveniles.

Net Production and Incerement in Stock of the Porphyra Community in the Culture Ground

Changes in the factors controlling the growth of the Porphyra community such as photosynthesis, respiration, and the increment in stock with the progress of the culture season were investigated under natural conditions in order to elucidate the characteristics of growth of the community in the culture ground.Net production of the Porphyra community was calculated by subtracting the respiratory loss from the total gain by photosynthesis, and was compared with the increment in stock actually observed in the culture ground. Calculated net production coincided fairly well with the observed increment in stock in earlier period of algal growth. However, in later period the remarkable discrepancy was found between the calculated net production and the observed increment in stock. This suggests that a great part of net production was lost from the community.Gross and net primary production of the Porphyra community was estimated on net area basis (Table 2). The daily increment in stock was 2.3g dry weight/m2 net area/day for the average throughout the investigated period of two months. The observed maximum standing crop was 140g dry weight/m2 net area. In the present culture ground the total amount of losses during these two months was estimated to be more than twice as much as the maximum standing crop observed.