Freshwater fish faunas of 44 rivers (504 sites) flowing into the Seto In-land Sea in Hiroshima Prefecture, western Honshu, Japan, were analysed with se-lected environmental factors of rivers. The cluster analysis of fish fauna revealed that these rivers were divided into three groups: long-length, middle-length, and short-length of rivers. There was significant correlation between the river length and the total number of fish species. Such a pattern was clearer in the genuine freshwater fishes rather than in the diadromous fishes.
The effects of pool type fishways on stream fish distribution in the Ishizaki River, Hokkaido, Japan, were evaluated from the view point of population density, estimated by mark and recapture experiments. The population densities of six diadromous species (Salvelinus leucomaenis, Oncorhynchus masou, Gymnogobius urotaenia, Rhinogobius sp.CO, Cottus hangiongensis and Plecoglossus altivelis) were estimated, only S. leucomaenis occurring above check dams that lacked fishways. Three species (O. masou, P altivelis and R. sp.CO) were present above dams with associated fishways, but their population densities were fre-quently lower than below the dams. G. urotaenia and C. hangiongensis were col-lected only below dams with fishways, whereas S. leucomaenis was present above dams that lacked fishways, suggesting that they were landlocked by those dams. It was concluded that pool type fishways are not necessarily the best aid for the mi-gration of diadromous fishes, most benthic fishes, in fact, not being able to use them.
Seasonal changes in the number and maturity of fishes ascending the Ogawa paddy field ditch in the Naka River system, Tochigi Prefecture, central Japan, were recorded from April to October in 1999 and from April to September in 2000. Totals of 949 fishes, representing 17 species and 745 fishes (12 species) were trapped in 1999 and 2000, respectively. Gnathopogon elongatus elongatus, Misgurnus anguillicaudatus and Pseudobagrus tokiensis were dominant in both years. Most individuals of G. elongatus elongatus, Cobitis biwae and Rhinogobius sp.OR were caught from late Spring (April) to early summer (June), most being mature. Pseudobagrus tokiensis, Silurus asotus and Zacco platypus were caught in summer (June-August), most also being mature. Zacco temminckii and Tribolodon hakonensis (mostly juveniles) were caught in summer and autumn (July-October). Mature and juvenile Misgurnus anguillicaudatus were caught throughout the study period (April-October). The results indicated varying periods and purposes for ditch ascent among the species, the ditches clearly being important in maintaining the biodiversity of freshwater fishes in paddy fields.
The unfertilized egg of Ammodytes personatus was small spherical and has the adhesive membrane developed from the zona radiata externa covering en-tire surface. This membrane is composed of the adhesive projection of cylindrical structures of many filaments and basement layer with regular arrangement of small holes. The adhesive membrane of the fertilized egg showed tongue-like structure transformed from adhesive filament. When attached to substrates, the tips of the adhesive filament are subjected to adhesive types of transformation. The spermato-zoon was about 25μm in total length, which comprised the asymmetrically elon-gated nucleus with the hiatus near the top, a single small mitochondrion and a sin-gle flagellum. The mitochondrion was located at the posterior side of the elongated nucleus, abutting the flagellum. The flagellum showed the typical 9+2 structure and was remarkably swollen. The A-tubules of doublets 1, 2, 5 and 6 contained a dense substance. The sperm showed a progressive speed of 85.5μm/sec. In seawa-ter, the spermatozoa usually maintained a circular motion for 20sec. Morphologi-cal and/or motility characteristics of gametes are discussed in relation to the func-tional aspects which are probably associated with the unique mode of spawning of this species.
To elucidate the feeding habits of smallmouth bass Micropterus dolomieu in Japanese inland waters, the stomach contents of fish from Lakes Aoki and Nojiri, Nagano Prefecture, differing in catchment landscape, were analyzed. Specimens were collected from May 2000 to October 2001 in Lake Aoki and from June to December 2000 in Lake Nojiri. Prey importance was estimated from an index of relative importance (IRI, (percent of prey number+percent of prey weight) ×frequency of prey occurrence). The main prey in Lake Aoki were pond smelt (Hypomesus nipponensis) and a cyprinid (Tribolodon hakonensis), and in Lake Nojiri, a shrimp (Macrobrachium nipponense) and goby (Rhinogobius sp.). Aquatic and terrestrial insects were also important prey in spring and summer in both lakes. Principal prey changed ontogenetically from small bottom-dwelling an-imals (gobies or aquatic insects) to larger limnetic fish in both lakes. The results suggested that smallmouth bass will have deleterious effects on differing animal groups with growth.
The taxonomic status between two Japanese cyprinids, Phoxinus lagowskii steindachneri and P. oxycephalus jouyi has been quite vague because of their resemblance of outer features to each other. The two forms from the four sympatric rivers were inspected to confirm the relationships between both as dis-tinct biological species on the basis of biochemical and morphological analyses. As a result they could be completely divided into two distinct groups in genetic and morphological characters, which taxonomically match P. lagowskii stein-dachneri and P. oxycephalus jouyi, respectively. The present study suggested the presence of reproductive isolation between the two species, and revealed that large local variation and secondary sexual characters in each species had contributed to taxonomic confusion.
We examined the selectivity of spawning habitat for shishamo smelt (Spirinchus lanceolatus) in December 2001 at pools and riffles of the Pon-warui stream, located in southern Hokkaido, Japan. We analyzed the sampling sites of fertilized shishamo smelt eggs in relation to environmental variables using princi-pal component analysis and ANOVA. The results showed that the eggs were dis-tributed to the pools with shallow (2-22cm), slow moving water (-0.07-0.10m/sec) and fine substrate (sand: particle size<2mm). The eggs are normally dis-persed downstream from the spawning ground (riffle or glide) by the stream cur-rent and should settle down against the bank of pools, highlighting the importance of preserving the pool-riffle sequence throughout the river system.
A single specimen of Rogadius tuberculatus (Cuvier, 1829) (URM-P 15156, 64.8 mm SL) was collected from Nakagusuku Bay, Okinawa Island, south-ern Japan in 1985. Characterized by many spines and tubercles on the dorsal sur-face of the head, the suborbital ridge finely serrated, 2-4 preorbital spines, well-de-veloped sensory tubes on the cheek region, no antrorse preopercular spines, 11 dorsal and anal fin soft rays, 52 lateral line scales with two exterior openings, the anteriormost 21 lateral line scales with a spine and 1+7=8 gill rakers, the speci-men represents the first record of the species from Japan and northernmost record from the western Pacific.
Phylogenetic relationships among 4 major geographic population groups (San-in-Biwa-Ise, East Seto, West Seto and West Kyushu) of Japanese freshwater goby Odontobutis obscura (Perciformes: Gobioidei: Odontobutidae) and related species O. hikimius were inferred from partial nucleotide sequences of the mitochondrial 12S and 16S rRNA genes. The resultant mitochondrial DNA (mtDNA) phylogeny was consistent with that based on the previous allozyme analysis. This phylogeny showed that specimens from the Sagami River system in Kanagawa Prefecture, Kanto District, were extremely close to fish from the West Seto group, suggesting the formers to have been descended from individuals artifi-cially introduced from the range of the latters. Judging from the fact that about 40 individuals of the goby were easily collected by a person in 2 hrs, the Kanto popu-lation did not seem to be small, and thus might be disturbing the native fauna in the river system.