A new ogcocephalid fish, Dibranchus japonicus, is described from deep waters around Japan.The species differs from other members of the genus in having a toothless vomer and palatine, spines moderately developed on the body, a circular disk, blackish body and fins without any blotches, in addition to some proportional measurements.This new species is the first discovery of a member of the genus Dibranchus from Japanese waters.

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Mating habits of the viviparous surfperch, Ditrema temmincki, were observed underwater with the help of SCUBA on the northern coast of Kyushu, Japan, during the period from 1977 to 1979.The mating season of the fish lasted from early September to early December.During the season, the fish moved into depths of 0.5-5.0 m, and large males over 1 year in age set up territories of 5-10 m in diameter.Females of nearly the same body length as males visited territories everyday.When females appeared in a territory, the male displayed by marked body color change and head-lowering posture.The territorial behavior and color change in small males under 1 year in age were not conspicuous in comparison with large males.After a repeated pre-copulatory behavior, copulation was accomplished between the sexes of nearly the same body length by contacting anal regions for a short time.Although courtship display of males and pre-copulatory behavior were seen frequently, copulation was seen only infrequently.The relationship between the mating season and occurrence of spermatozoa in ovaries is discussed.

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Chirolophis saitone (Jordan et Snyder, 1902) is redescribed based on newly collected specimens, i.e., six specimens (55.0-82.0 mm SL) from Mutsu Bay, Aomori and two specimens (61.3, 71.0 mm SL) from Hokkaido, northern Japan and on the holotype.It is diagnosed from its congeners mainly by teeth with pointed tips, smaller numbers of occipital sensory canal openings and the mossy head.

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The mature spermatozoon of Lampetra japonica is about 130μm long.The head is rodshaped, measuring about 8μm long and 1μm wide. It bears a membrane-bounded acrosomal vesicle at its anterior end.The anterior surface of the nucleus in the head forms a depression, where a subacrosomal ring is found.The bottom of the depression leads to the nuclear canal.The central fiber, which starts from the posterior surface of the acrosomal vesicle, perforates the subacro-somal ring and runs the entire length of the nuclear canal.The elongated nucleus forms a pouch laterally near the posterior end of the head, where two cylindrical centrioles are visible;the axes of both centrioles coincide with a long axis of the spermatozoon.The tail flagellum shows the 9 +9 +2 structure known in that of animals with internal fertilization.There is no strictly defined middle piece, but several mitochondria are detected near the centrioles or in regions far from the snerm head.
An acrosomal filament is formed in some spermatozoa when they are subjected to stimulation at the time of fixation: the central fiber is discharged from the nuclear canal and pushes against the posterior membrane of the acrosomal vesicle;this induces the fusion of the anterior membrane of the acrosomal vesicle with the plasma membrane.The acrosomal filament thus formed consists of the central fiber and its surrounding membrane.No changes in the morphology of the subacrosomal ring are detected during the filament formation.We conclude that the acrosome reaction closely resembles that reported in certain molluscs and annelids which have an axial rod in the head.

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Nocturnal activities in the catfish Silurus asotus were investigated experimentally with an actograph.Most of their nocturnal action commenced nearly at or soon after sunset when ambient light intensities were close to 0.001 lux at various water temperatures (10°-25°C) under natural light conditions.Their nocturnal action, however, terminated a little or more before sunrise depending on the difference of water temperature, when the ambient light intensities were 0.0001 lux or less.The nocturnal activities of this catfish were controlled not only by the daily changes in the ambient light but also by an endogenous circadian rhythm which was detected in light: dark pulses repeated with a short period, and in constant darkness.Their daily activities in nature were regarded as a result of synchronous cooperation of the endogeneous rhythmical system and daily light: dark stimuli.

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Four dicephalous specimens of the blue shark, Prionace glauca, were obtained from Choshi, Kumanonada, Sendai and Torishima, Japan.All of the specimens were dicephalus, duplicitas anterior, duplicitas symmetros, conjoined twins.
Choshi specimen (_??_): Left and right heads are almost the same in size and shape, and conjoin with each lateral surface at the fifth gill opening.Total lengths are 171 mm for the right and 170 mm for the left individuals.Each head has nostrils, eyes, a mouth and the first and second dorsal fins.There are only a single pair of pectoral, pelvic and one anal fins and one umbilical cord.The caudal fin has three ventral lobes, that is for three individuals, which fuse into one dorsal lobe.The caudal portion from the second dorsal and anal fins bends to the right at an angle of 150°.Dimensions of body parts of the left and right individuals are almost the same.In radiograph, two vertebrate columns exist in the cranial portion from near the origin of the second dorsal fin, and they fuse into one in the caudal region.
Kumanonada specimen (_??_): Left head is shorter than right head.Total lengths are 250 mm for the left and 222 mm for the right.The left and right heads are conjoined with each lateroventral surface near the fifth gill opening.Nostrils, eyes, mouth and the first and second dorsal fins are for two individuals, but there are only a single pair of pectoral and pelvic fins, a single anal fin, and one umbilical cord.The caudal portion from the second dorsal and anal fins is screw-shaped.The left is larger than the right in dimensions of total length, mouth, eyes, gill openings, first dorsal fin, etc.In radiograph, two vertebral columns exist from the caudal end of the chondrocranium to the tip of the caudal fin which is spiraled.The right ventral column bends ventrally near the pectoral fin and dorsally near the first dorsal fin and curves near the pelvic fin.
Torishima specimen (_??_): Left and right heads are almost the same in size and shape, and conjoin with each laterodorsal surface at the fourth gill opening.Total lengths are 107 mm for the left and 108 mm for the right.Nostrils, eyes and mouth represent two individuals.The mouth of the left head is smaller than that of right and lacks lower jaw cartilage (Meckel's cartilage) and lower dentition.The right eye of the right head is very large.The first and second dorsal, anal, caudal, pectoral and pelvic fins and umbilical cord are for one individual.The caudal portion from the first dorsal fin is considerably screw-shaped.Dimensions of body parts of the left and right in-dividuals are nearly the same.In radiograph, two vertebral columns exist in the cranial portion from near the origin of the first dorsal fin and in the caudal portion they fuse into one.Both left and right vertebral columns bend dorsally at the cranial position of the first dorsal fin.In the caudal portion from the first dorsal fin, the vertebral column spirals.
Sendai specimen (_??_): This specimen is similar to the Torishima specimen, but both jaws, teeth and eyes are normal.Total lengths are 120 mm on the left and 115 mm on the right.
These four dicephalous specimens of Prionace glauca (Chondrichthyes) were compared with the dicephalous specimens of other vertebrates, Chrysemys scripta (Reptilia), Agkistrodon halys (Reptilia), Bos taurus (Mammalia) and Homo sapiens.The fusion and separation of vertebral columns vary considerably.But, it can be noted that some anomalies of vertebral column, for example, bending and curving, are observed in many cases of dicephalous in various vertebrates.

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[in Japanese]

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[in Japanese]

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Three specimens of the amago salmon, Oncorhynchus rhodurus, were caught off Chikubu Island in Lake Biwa, Shiga Prefecture, Japan. These specimens were females measuring 260-375 mm in standard length, with red spots on both sides of the body.The transverse scale counts above the lateral line were 27-32.Ridges of scales had disappeared in the apical margin of the scales.These characters resemble those of the amago salmon found in the Nagara River or Lake Suwa, and differ from those of the Biwa salmon found in Lake Biwa (Kato, 1973a, 1975a, b, 1978).Therefore the author identified the specimens as amago salmon.They are presumed to have descended in the smolt stage into Lake Biwa and to have grown there.

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Numerous specimens of Cobitis taenia were collected from Mie and Shizuoka Prefectures, central Honshu, Japan.These specimens were compared morphologically with syntopic specimens of C. biwaev Predorsal distance, length of barbels and number and composition of vertebrae, in addition to the shape of the lamina circularis, were helpful in distinguishing between these two forms from the same localities.Morphological and taxonomical problems concerning two subspecies of C.taenia from Japan are discussed.

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Three males and 3 females of the chum salmon, Oncorhynchus keta (Walbaum), were collected from shore waters and streams in Fukuoka and Saga Pre-fectures in northern Kyushu.Their photographs, measurements, counts, dates of capture and localities are shown in this paper.All of the present specimens had attained maturity; especially the females caught in the Tamashima and Onga Rivers had eggs fully matured.In the basins of these rivers, it is said that almost every year a very small run of the chums had been observed in the Tamashima River before the 1950's and also in the Onga River before the 1920's.The Tamashima River, flowing through the northern territory of Saga Prefecture, is at present the south-westernmost record of the return of the chum salmon in Japan.

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Eighty-four specimens of a gobiid fish, Paleatogohius uchidai Takagi, were collected in Usu Bay (42° 30'N, 140°45'E), Hokkaido in 1980, Since this species has been known only from Kyushu district, the collections from Usu Bay are a new record for Hokkaido, which is far north of the localities previously recorded.The presence of some common environmental factors for the type locality and Usu Bay, as well as the occurrence of mature females and many juveniles in August, suggests that this species. breeds in Usu Bay.

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