"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 per mille - 21 per mille 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."
The embryonic development of Plecoglossus altivelis altivelis was described on the basis of eggs inseminated artificially on October 24, 1984 in Lake Ikeda. The eggs were spherical, 0.87-0.92mm in ...diameter. The incubationp eriod was about 230 hours at a water tempera-ture of 14.5-23.2°C (av. 20.1°C). The standard length newly hatched larvae had a small yolk sac (av. 5.3mm) and 61-62 myotomes. Within several days of hatching, the larvae attained 6.0-7.9mm in standard length and had completely consumed their yolk substances. Morphological changes of the larvae accompanying their growth were observed on 1.263 specimens collected by the larval net (80cm in diameter, 0.353 in meshes), the surf zone net (1m×5m, 1mm) and the cast net (13mm). The larval fin fold gradually disappeared, and the rudimental dorsal, the anal, the ventral and the adipose fins were visible at 11.4, 12.8, 24.3, 44.5mm in standard length, respectively. The conical teeth appeared at 24.3mm and the comb-like teeth at 55mm. Larvae smaller than 25mm inhabited the offshore waters of the lake, while those larger than 27mm appeared in the surf zone of the lake shore. The vertebral centrums of the larvae ossified at a size of 27.3mm. It is suggested that the considerable morphological changes of the ayu occurred at sizes of 25-30mm and 50-55mm in standard length. The former corresponds to the end of the larval stage and the latter to the end of the juvenile stage, respectively.
Distribution areas of larvae and early juveniles of Trachidermis fasciatus were investigated in the northern Ariake Sound and the fluenting Kashima River waters during the period from February to May ...in 1994. The larvae (7 16mm TL) appeared at stations near the coasts of the Ariake Sound where salinities ranged from 16 to 25 ppt and larvae and pelagic juveniles (13 20mm TL) appeared in stations from the mouth of the Kashima River to 3km upstream ranging from 3 to 25 ppt in salinities. The settled juveniles were collected at stations in the river where salinities were almost 0 during low tide. Early larvae, pelagic juveniles, and settled juveniles hatched and reared in aquaria were exposed to various salinity conditions (0, 11, 23, and 34 ppt). Larvae most rapidly grew at 34 ppt, but settled juveniles more rapidly grew and their survival rates were higher in low salinities.
The yearlings of a cyprinid fish Hemibarbus barbus of the Chikugo River, Kyushu, Japan, mi-grate down to the lower reaches and further to the freshwater area of tidal reaches within a year after ...hatching. After staying there for 3-4 years, mature fish run up to the middle reaches for spawning in spring. In order to elucidate the feeding habit of H. barbus, we examined the gut contents of 822 specimens collected during 1986 and 1987. The yearling 10-20mm in standard length (SL) fed on zoo-plankton (rotifers, cladocerans, copepods), and that of 20-40mm SL fed on mainly copepods in the lower reaches. Depending on their growth, they gradually changed feeding items from zoo-plankton to benthic animals such as chironomid larvae. Then, the yearling over 50mm SL having pharyngeal bones which formed the same shape as those of adult fish began to crush and feed on corbiculids and ephemerid larvae. After migrating down to the tidal reaches, they also fed on benthic animals (chironomid larvae, corbiculids, polychaetes). Elvers of the Japanese eel Anguilla japonica and the young mitten crab Eriocheir japonicus occurred in the guts of 2-year-old and older fish.
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