Somatic chromosomes of the nigorobuna (C.auratus grandoculis) obtained from Lake Biwa, two local varieties of the nagabuna (C.auratus buergeri) from Lake Suwa and the Hokkaido district, and two local varieties of the ginbuna (C.auratus langsdorfii) from the Okayama Prefecture and Lake Biwa were studied and compared.Chromosome preparations was performed by the same methods previously described (Kobayasi et al., 1970). The results showed that the nigorobuna and nagabuna of Lake Suwa and the ginbuna of the Okayama Prefecture had the same diploid chromosome number of 100.Their karyotypes consisted of 10 pairs of metacentrics, 20 pairs of submetacentrics and 20 pairs of acrocentric elements.There was no morphological difference between the male and female karyotypes. On the other hand, 5 females of the nagabuna collected from the Hokkaido district and 4 females of the ginbuna (hiwara) from Lake Biwa had the chromosome number of 156, consisting of 17 pairs of metacentrics, 31 pairs of submetacentrics and 30 pairs of acrocentrics. The populations of the ginbuna and nagabuna in these regions consisted mostly or almost entirely of females.It was proved from these evidences that the nagabuna and ginbuna with triploid state occur not only in the Kanto district but also in the Hokkaido district and Lake Biwa.These triproid females might be arisen by gynogenesis, as has been reported in the ginbuna obtained from the KantO district by Kobayasi (1971) and Kobayasi and Ochi (1972). [Japan Women's University, Bunkyo-ku, Tokyo, 112, Japan (H.K.and H.O.);National Science Museum, Hyakunin-cho, Shinjuku-ku, Tokyo, 160, Japan (N.T.)]
Sand samples from the bottom of the fishing ground of Salangichthys microdon in the Takahashi estuary were collected from 33 stations for the examination of naturally spawned eggs of the fish. The eggs were found among sand grains collected from 7 stations. Eggs were most abundant, 870 eggs per300ml sand grains, at the sand bar exposed only at the low tide and is located near the estuary dam, 5.2km upstream from the river mouth.The next highest density, 238 eggs per 300ml sand grains, was observed at the station near the river mouth.Eggs at various developmental stages were observed.The eggs, even those in the sand bar, were found to be developing successfully in spite of the wide range of fluctuation of chlorinity (0.8‰, at low tides to 16.8‰, at high tides).The spawning ground is mainly composed of sand grains ranging from one-third to equal diameter of eggs (0.92-0.95 mm). No eggs were found to be attached to the thalli of the sea-weed, Enteromorpha prolifera, which flourished on the concrete floor of the dam and on the rubble mound below it. However, in lakes such as Kasumigaura, it has long been believed that the fish lay their eggs on the stems and leaves of aquatic plants.This difference in the spawning habits may be attributed to the difference of water currents.Since there are relatively few records of the collection of naturally spawned eggs in lakes, further investigation is essential to confirm whether the fish in lakes do not lay their eggs into sand.
Four-armed scoop net fishery for Salangichthys microdon Bleeker is operated in the Takahashi estuary, Okayama Prefecture, yielding 10-17 tons of the fish annually.Although the daily catch per boat averaged 7-8kg during the main fishing season, February to March, the catch fluctuated considerably and irregularly without obvious relationship with the lunar calendar or the tidal conditions.The fish caught in this fishing ground were rather large in size.The condition factor of the fish was found to be high.Females exceed the males in body length, but reversed in body weight.An inverse correlation between the gonad index and the condition factor was not found in individual fish, though a decrease in the condition factor after spawning was obvious for the group as a whole.About 1300 to 2700 eggs were counted in a pair of ovaries. There was no clear correlation between the number of ovarian eggs and the body length or the body weight of the fish.Larvae of a gobiid fish, Chaenogobius sp.as well as mysid shrimps, Neomysis sp.were found in the digestive organs of the fish.
The tripterygiid blenny, Tripterygion etheostoma Jordan and Snyder is one of the common blennies in the rocky shore of the central and southern Japan.It feeds on creeping copepods, tiny shells, crab larvae, and annelid larvae.It grows to 60mm in full grown size. It shows the sexual dimorphism in coloration.The spawning season seems to extend from April to November in the shore of Nomozaki (Lat.32°35.3'N, Long.129°45.5'E), near Nagasaki. From the rocky shore of Nomozaki, 34 adults, comprising 11 males and 23 females were collected and kept in a table aquarium for the spawning experiment during the period from March 27 to November 19, 1971.During the above period, 21 spawnings were observed in the aquarium. In the actual spawning, a male parent first occupied one of the six stones previously set on the aquarium bottom for the spawning bed and guarded the stones for the fish intruders.The male cleaned filaments of the tiny prostrate alga, Gelidium pusillum growing on the stone surface.A female came to the boundary of the stone and displayed itself to the male.The male induced the female to the algal zone on the stone.After the pairing, the male instantly demonstrated quick half-circling movement around the algal zone.The female entered into the center of the movement and spawned the first egg there. The female rather sparsely deposited the eggs among the algal filaments on the stone spawning bed at intervals 17 to 69 sec.The inseminating behavior of the male instantly followed each oviposition. After the spawning, the female left the spawning bed, whereas the male guarded eggs without fanning action. Four of 11 males kept in the aquarium alternatively participated in 3 to 9 spawnings by various females in the period from 4 to 39 days.In a spawning, there were several egg masses in different developmental stages and each egg mass comprised from 24 to 518 eggs. The eggs were about 1 mm in average diameter, and each egg was provided with sticky filaments entangled on algal filaments growing on the stone spawning bed. An egg mass deposited among filaments of tiny prostrate algae, comprising Herposiphonia tenella and others, was collected from a tide pool on the rocky shore of Nomozaki on August 24, 1972, together with the male parent guarding it.
The egg development of the tripterigiid blenny, Tripterygyon etheostoma Jordan and Snyder was observed with the eggs laid in an aquarium of the Fisheries Experimental Station of Nagasaki University in Nomozaki (Lat.32°35.3'N, Long.129°45.5'E) during April to May, 1971. The eggs were semi-spherical in shape and ranged from 0.90 to 1.03mm in diameter. Each egg was provided with numerous sticky filaments entangled to the prostrate alga, Gelidum pusillum growing on the stone. The color of the yolk was light yellowish orange in the early developmental stage, then turned to orange in the eye-formation stage, and then to reddish orange in the eye pigmnented stage.The yolk contained numerous tiny oil globules crowded to the animal pole side. The hatching took place within 390 hours after spawning at the temperature varying from 15.7 to 18.2°C. Newly hatched prolarvae were elongate in shape and 4.57 to 5.00mm in total length. The larvae were kept in a 30 liter plastic aquarium and fed with the nauplii of the barnacle, Balanus amphitrite amphitrite and then with the mixture of the rotifer, Brachionus plicatilis and the nauplii of the brine shrimp, Artemia salina.The larvae spent the planktonic life for about 40 days and entered into the bottom life at about 12 mm Juvenescent stage. The 236 specimens of the blenny, comprising the larvae and juveniles, ranging from 2.9 to 12.0mm in total length were collected with submerged fish lamp in Noma Bay, Nomozaki from 1968 to 1969.It seemed that the larvae were drifted by tidal current to the bay from the neighboring coast where the blenny commonly lived.
Two Oplegnathus juveniles were found among shoals of juveniles attached to the floating patches of seaweeds migrating to Oshima waters in 1969 to 1970.Under investigation of their morphological characteristics, they are presumed to be hybrids between O.fasciatus and O.punctatus, both of which are common in waters of central Japan.