Development and distribution of larval zaprorid fish, Zaprora silenus Jordan, from the Bering Sea and around the Aleutian Islands are described.A total of 31 specimens of larvae, ranging in body length from 12.0 to 36.2mm, were collected with a 1.3-m ring net at 12 stations from June to August, 1971-1979. Zaprora silenus is characterized by the dense pigmentation of black and brown stellate melano-phores which are found on the sides of the body through the larval period.The anus is located a little behind the middle of the body.Larvae were classified in three developmental stages: larval, prejuvenile, and juvenile stages.These included nine specimens excluding the minimum larva which was immeasurable, ranging in body length from 12.0 to 17.3mm, 10 specimens from 17.5 to 24.0mm, and 11 specimens from 26.9 to 36.2mm, respectively.In the larval stage of 17.3mm in length the body is surrounded by the fin fold, and the notochord is slightly flexed and 16 rays appear in the caudal area.Melanophores are present in the fin fold of the anal fin area.In the early prejuvenile stage the caudal elements are well developed.In the late stage the notochord is fully flexed and the caudal fin is formed.Although the full number of rays for each fin is present, the dorsal and anal fins still connect with the caudal fin.Several pigment bands appear on the dorsal and anal fins.In the juvenile stage each fin is completed and body proportions become constant.Seven to eight bands of pigment appear on the dorsal and three bands on the anal fin. Two larvae were taken in the Pacific side of the Aleutian Islands, south of the Amchitka and Atka Islands.In the Bering Sea two specimens were collected north of the Tanaga and Adak Islands, and 25 specimens were captured above the 30m layer in the slope region at depths of 150 to 3000m from Unalaska Island to the Pribilof Islands.Two larvae were also collected in the basin area (latitude 58°N).The distributional pattern suggests that Zaprora silenus is planktonic during the larval and juvenile stages in the upper layer within the Alaskan Stream and the Bering Slope Current.
Opisthocentrus tenuis Bean and Bean, 1897, is known from Hokkaido, Mutsu Bay, Aomori Pref., Iwate Pref.and Sado Island in Niigata Pref.This species dwells in small schools among Zostera in Mutsu Bay.It feeds mainly on benthic gammarids and caprellids, and usually swims slowly above the bottom in an L-shaped posture by fanning its large pectoral fins. In Mutsu Bay, the spawning period seems to extend from early December to late January.The water temperature during this period falls to 5-10°C. From experiences with spawning experiments in the aquarium and observations on natural egg masses, the egg mass is always guarded by the spawned female.For studies in a small aquarium, a vinyl pipe was used as the spawning nest.In the natural site at Moura, Mutsu Bay, 5 to 6 m deep, each egg mass was found with the female parent coiled about it in a nest on the stony bottom.A female spawns only one time in one spawning season. Eggs are attached to each other by their adhesive points, though they have no adhesive processes, and form a single spherical egg mass about 3 cm in diameter.The egg is translucent.The yolk is colorless, containing a large light yellow oil globule and many small ones with white cloudy materials surrounding the large oil globule.The egg membrane is about 2_3 mm in diameter. Eggs spawned in the aquarium developed in water temperature varing from 4.6 to 8.0°C and larvae hatched about 58 to 64 days after the spawning.Newly hatched prolarvae, provided with large remnants of yolk, are slender and 11.0 to 11.8 mm in total length.The newly hatched prolarvae reach the postlarval stage about 20 days after hatching.Hatched larvae were reared in a small vessel for about two months.They were fed nauplii of brine shrimp Artemia sp., but the largest one reached only 19.0mm. In May, 1979, at Moura, young fish, some more than 3 cm TL., were observed swimming close to the bottom in schools.From examinations of over four hundred specimens collected from Mutsu Bay, one year old fish seemed to grow to 6 to 10 cm TL., two year olds to 11 to 15 cm and three year olds to 16 to 19cm.Most fish attain sexual maturity in two years.The life span is two years in most fish.
The examination of a species of Japanese gobiid fishes with five branchiostegals and completely separated pelvic fins revealed that it agrees well with the holotype of Riukiuia poecila Fowler, 1946, known only from the holotype.The fact that no specimen has been identified as R.poecila since 1946 is considered to be due to the original description, where R.poecila is described as having five dorsal spines, whereas the holotype actually has six. Smith (1958) synonymized the genera Leioeleotris Fowler, 1934 (type species: L. zonatus) and Riukiuia Fowler, 1946 (type species: R.poecila) with Hetereleotris Bleeker, 1874 (type species: Gobius diadematus).As a result of our examination of the type species of the genera Hetereleotris, Leioeleotris, Lioteres Smith, 1958 (type species: L.caminatus), Chriolepidops Smith, 1958 (type species: C.nebulopunctatus), Satulinus Smith, 1958 (type species: S.zanzibarensis), and Dactyleleotris Smith, 1958 (type species: D.tentaculatus), and the subgenus Pseudolioteres (type species: Lioteres (P.) simulans which is synonymous with H.diadematus), we conclude that all of these should be included in the genus Hetereleotris, because they all share such common characteristics as protruding anterior and posterior nostrils, the first gill arch with most of the lower limb covered by membrane, broad isthmus and gill membrane attached to the base of pectoral fin, six dorsal spines, segmented caudal fin rays 9+8=17, completely separated pelvic fins without a frenum or a uniting membrane between them, five branchiostegals, vertebrae 10+17=27, first and second pterygiophores of first dorsal fin inserted between neural spines of third and fourth vertebrae and the last between those of sixth and seventh vertebrae, first and second pterygiophores of second dorsal fin spanning neural spine of ninth vertebra, an epural, and four transverse pit organ lines below eye and a longitudinal pit organ line touching the lower tips of the first three transverse pit organ lines and running to the fourth transverse pit organ line. The relationship between the genus Hetereleotris and the genera Chriolepis, Eleotrica, and Gymneleotris of the seven-spined gobies of the Americas, which are said to be related to the genus Hetereleotris by Smith (1958), is not considered to be close, because, in addition to other differences, the genus Hetereleotris has a membrane covering the first gill slit, which is not found in these genera of the seven-spined gobies.The osteological comparison of H.poecila and H.zonatus with the genera Aruma, Pycnomma, and Gymneleotris of the sevenspined gobies revealed that, although the pelvic girdle of the genus Gymneleotris resembles the genus Hetereleotris, this, characteristic is not consistent in the other closely related genera Aruma and Pycnomma.This characteristic, therefore, does not seem to have any value in considering their relationship. Pelvic fins without a frenum and with a vestigial condition of the uniting membrane are found in the various phylogenetic groups of gobiid fishes with five branchiostegals, but in these groups pelvic fins without a uniting membrane have been found only in the genus Hetereleotris. The genus Hetereleotris is thus considered to be unique among the gobiid fishes with five branchiostegals, in having no closely related genera.
Shapes of the swim bladders were studied for clarifying differences in three species of the genus Tribolodon, T.hakonensis (Günther), T.taczanowskii (Steindachner) and T.ezoe Okada et Ikeda, taken from several localities in Hokkaido. The feature of the tip of the posterior chamber of the swim bladder, with two types, is useful to distinguish between T.ezoe (round or grainy tip) on the one hand and T. hakonensis and T.taczanowskii (tapering or sharp tip) on the other hand. The length of the posterior chamber of the swim bladder was also different among the three species, i.e., it is longest in T.hakonensis, shortest in T.ezoe, and intermediate in T.taczanowskii.