To clarify the early life history of a fluviatile goby (“Kibara-yoshinobori”) Rhinogobius sp.YB, the morphological characters of newly hatched larva and distribution pattern of larvae were investigated, while collecting the eggs and drifting larvae from March 2000 to April 2002 at four stations in the upper stream of Sumiyo River, Amami-oshima Island, southern Japan. Judging from the appearance of clutch of eggs and larvae, the breeding period was assumed to last for three months from April to June with a peak in May. The egg diameter was larger than that from Okinawa-jima Island and any other waters of Amami-oshima Island. Thelar gest embryos collected from egg clutch showed a postflexion stage, forming second dorsal, anal and principal caudal fin rays. These characters denoted a more advanced stage than previously reported. The larvae gathered in the shallow water area (<40 cm) with low current velocity (<5 cm/s) near shore and around substratum. The swimming ability of the newly hatched larvae and characteristic distribution of the larvae reduced a carry-away risk and thus enabled their life history within stream.
The distribution and population density of the endangered mudskipper, Boleophthalmus pectinirostris, in estuaries in Ariake and Yatsushiro Bay, were surveyed in September, 2003. The species was observed at 108 of 197 surveyed locations in Ariake Bay and 14 of 39 locations in Yatsushiro Bay. Comparison with the previous investigation in 1991 indicated a small distribution extension, although, the population in the inner part of Isahaya Bay (Ariake Bay) was likely to be extinct, undoubtedly due to the Isahaya Bay reclamation project, which has resulted in more than 80% loss of estuarine habitats in that part of Nagasaki Prefecture. In most areas except for the inner part of Isahaya Bay, both distribution and population density of B. pectinirostris have shown a tendency to increase since the middle 1980s, when the species was in a very serious condition. But, past dynamics of both distribution and population density indicate the possibility that they fluctuate several-year time scale, showing that a species and habitat protection policy for B. pectinirostris should be established in all areas, as has been done for the Saga Prefecture portion of Ariake Bay.
Clutch and egg size in the Japanese amphidromous goby, Rhinogobius sp.DA (R. brunneus, dark type), inhabiting small rivers in the southern part of the Kii peninsula were examined. Clutch sizes, ranging between 1043 and 4436, increased with increasing maternal standard length. Spawned egg volume ranged between 0.85 mm3 and 1.38 mm3, mean egg volumes being similar among the eight rivers sampled during the study. Rhinogobius sp.DA had a relatively larger egg and smaller clutch size compared to those of three other amphidromous Rhinogobius species inhabiting relatively larger rivers in the same region. Inter-specihic egg size variations among the four species appear to result in differing larval survival rates during their migration to the sea.
Phoxinus lagowskii yamamotis is a small dace-like cyprinid, endemic to Lakes Yamanaka and Motosu at the northern base of Mt. Fuji. The fish was categorized as Data Deficient (DD) in the Japanese Red Data Book (2nd edition). Morphological comparisons between the type series of “Moroco yamamotis” and syntypes of “P.steindachneri” revealed a distinction in caudal peduncle height, the former showing extreme values, lower than for other individuals from same river basin and adjacent rivers. Phoxinus lagowskii yamamotis may have been a lacustrine population from which an ancestoral population of P.lagowskii steindachneri evolved following adaptations to a lentic environment. Several specimens were collected from an outlet of L. Yamanaka. A relationship between these specimens and the lacustrine “M.yamamotis” group is suggested, the assemblage being in need of conservation as an evolutionarily significant unit.
A single specimen (HUMZ 177334, 88.5 mm in standard length) of a stichaeid fish, Leptoclinus maculatus diaphanocarus (Schmidt, 1904), was trawled in depths of 121.4-121.6m, inOkhotsk Sea, off Esashi in the northern part of Hokkaido, in August 1999. It represents the first reliable record of the subspecies based on the specimen from Japan and the southernmost record of the subspecies. Previous confusion about Japanese names for two subspecies of L. maculatus was reviewed.
The endangered amphidromous goby, Rhinogobius sp.BI, is the only freshwater fish endemic to the Bonin islands. Ex situ aquaculture, conducted over a number of generations, should be undertaken so as to ensure future protection of the species. Salinity being one of the most important larval-rearing factors, experiment was conducted on the salinity tolerance of hatching larvae. These could generally survive for 72 hours under any salinity conditions. However, all individuals died after 144 hours in 100% artificial seawater, whereas over 60% survived for a longer term in freshwater and 50% artificial seawater. With decreasing salinity, the greater the survival duration time. However, larval numbers fell dramatically ca. 40 days after hatching in 50% artificial seawater, such a reduction in number indicating a critical depletion period in the early developmental stages.
A phylogenetic analysis, based on the complete nucleotide sequences of the mitochondorial control region (D-loop), was conducted on Mola mola occurring around the Japan coast. Two significantly distant clades (bootstrap value 914, based on 1000 replicates) were recognized. One consisted of 19 specimens with 812-814 by D-loop sequences that were collected from geographically wide spread locations around Japan (Aomori to Kagoshima). The other clade consisted of 3 specimens (all greater than 2 m in total length) collected from the Pacific coast of eastern Japan and characterized by 817 by D-loop sequences with many nucleotide substitutions compared with the former clade (ca.100 positions).
The genetic population structure of Rhynchocypris lagowskii steindachneri in three river systems flowing through Yokohama and adjacent areas in southwestern Kanto, central Honshu, Japan, was investigated by examination of nucleotide sequences of the mitochondrial DNA (mtDNA) control region. Although R. lagowskii steindachneri is the only Rhynchocypris species native to the region, the establishment of R. oxycephalus jouyi, which was artificially introduced in the late 1980's, was confirmed in one of the river systems investigated. From the same river system, one of 27 specimens (4%) of R. lagowskii steindachneri was found to have a R. oxycephalus jouyi mtDNA type, implying some genetic disturbance within the former population. Although the R. lagowskii steindachneri populations investigated, distributed within a 40-km geographic range, appeared to belong toa single phylogeographic group, significant differences in haplotype frequencies and diversity levels were found, probably being the result of genetic drift following recent artificial fragmentation and habitat reduction.
A single specimen of the derichthyid longneck eel, Derichthys serpentinus, was collected from midwater off Miyagi Prefecture, northwestern Pacific, Japan (HUMZ 182165, 288 mm in total length, near ripe female). The specimen was characterized by 252 dorsal fin rays, 165 anal fin rays, 132 vertebrae (total), a short snout and lower jaw, concave predorsal region, conspicuous head pores, many cicatrix-like dermal ridges on the head and a uniformly dark brown body. In Japanese waters, D. serpentinus has been previously recorded from the Kyushu-Palau Ridge (in the gut contents of a berycid, Beryx splendens) and the Ogasawara Islands (leptocephalus). The resent report, based on a near ripe specimen captured directly by trawl net, represents the first reliable record of the species from Japan and northernmost western Pacific record of the species.