Abstract Ultrastructural observations of spermiogenesis in two paedomorphic gobioid fishes, Schindleria sp. and Leucopsarion petersii, were discussed with special reference to the specialized morphology of their spermatozoa. In Schindleria sp., spermiogenesis was characterized by (1) apical vesicle generated from nuclear section and surrounded by cytoplasm, (2) flagellum implanted to centriole at base of nucleus, moving towards apical vesicle by piercing nucleus center to beyond nucleus tip, (3) apical vesicle spermatozoon subsequently disappearing, (4) nucleus of mature spermatozoon cylindrical, 3.2m m in length and ca. 0.5m m in width, (5)flagellum fully penetrating nucleus, resulting in sperm length equaling flagellum length and (6) single mitochondrion located at base of flagellum in contact with posterior end of nucleus. In Leucopsarion petersii, spermiogenesis was characterized by (1) a mass of small vesicles at nucleus tip forming apical point, (2) elongated apical point based on four rounded corners on top of ovoidal nucleus, (3) two centrioles located on basal body of nucleus, each with a typical flagellum, (4) both flagella with 92 axoneme pattern and (5) mitochondria varying in size and shape coalesce into a long midpiece. The spermatozoa of both species bear extremely specialized structures, such as the apical vesicle and the apical point, not yet reported in other teleosts. These structures are likely to have evolved within the less restricted framework of sperm morphology of gobioids, as reflected in the unusually high species diversity of this group.
Morphological and genetical analyses revealed a spined loach population from Tango District, Kyoto Prefecture, to be an allotetraploid form of Cobitis striata. The former had distinctive differences in body coloration and mitochondrial DNA sequences from another allotetraploid form of Cobitis striata, found inLake Biwa, and is tentatively termed the ‘Tango tetraploid form’ of C. striata.
Carassius auratus in the Ryukyu Archipelago includes both indigenous and introduced populations which can be discriminated from each other by mitochondrial DNA (mtDNA) haplotyping. MtDNA haplotyping of 485 fish from38 water systems on 11 islands within the Archipelago, showed them to comprise254 (52%) indigenous and 231 (48%) introduced individuals. Indigenous specimens were widespread throughout the Ryukyus, mainly inhabiting natural water systems. Introduced specimens were encountered sporadically, mainly in artificial water systems, especially in reservoirs. Ploidy examination by flow cytometry showed that indigenous populations comprised only diploid or diploid and triploid fish, whereas introduced populations often comprise only triploids. The fact that C. auratus was not found on some islands surveyed, despite their former presence being confirmed, suggested recent decreases of C. auratus and highlighted the importance of future conservation of indigenous Ryukyuan C. auratus.
Variations in genetic and morphological characteristics were investigated in two populations of the exotic pond loach, Paramisgurnus dabryanus, which has invaded rice fields in Kuma-kougen Town, Ehime Prefecture. A sequence analysis of the mitochondrial DNA control region of 46 individuals collectedf rom two sampling sites (Higashi-myoujin and Koudono, separation distance1.6 km) revealed two divergent clades (average nucleotide divergence: 15%)representing separate introductions: Group 1 (four haplotypes), related to P. dabryanus, and Group 2 (two haplotypes), related to Misgurnus anguillicaudatus, as a result of mitochondrial DNA introgression. In 29 of the 46 specimens, which included individuals of both genetic clades, four of 13 morphological characteristics(relative to body size) (head length, pre-pectoral length, dorsal fin base length and caudal peduncle depth) differed significantly (ANOVA, df 28, P 0.01-0.05)between populations, but not between genetic clades. Haplotype constitutions differed significantly between sampling sites (exact test, P 0.001), diversities being greater in Koudono which is located downstream of Higashi-myoujin. The existence of genetically divergent clades among the specimens suggested that the early introductions of this species to Japan originated from several localities.
Environmental factors affecting the preference of branch drainage ditches by round crucian carp (Carassius auratus grandoculis), a Lake Biwa endemic subspecies, were analyzed, fish often ascending to paddy fields, via drainage ditches, for spawning. A logistic regression analysis to determine facors influencing, drainage ditch selection showed dissolved oxygen to be significant, whereas turbidity and water velocity were not. Nevertheless, differences in distribution between ditches selected or not selected for spawning suggested that greater water velocity and moderate turbidity were also important factors.
In order to establish a feasible conservation program for the Itasenpara bittering (Acheilognathus longipinnis), the genetic population structure was determined on the basis of five microsatellite loci for wild and captive populations from Himi City, Toyama Prefecture, and the Yodo River system, Osaka Prefecture. An endemic genetic feature was found in each of the Toyama and Osaka regional populations, indicating that each should be treated as a separate unit in any future conservation program. The degree of genetic diversity in the Toyama populations tended to be lower than that in the Osaka population, being related to the population size and/or population demography. In the Toyama region, captive populations showed an equal degree of genetic diversity as the wild populations, probably due to a relatively short period of captive breeding as well as continuing introductions of wild individuals.
Bitterling are fishes that use freshwater mussels for oviposition. Mussel utilization by an endangered bitterling species, Acheilognathus tabira erythropterus, and an exotic species, Rhodeus ocellatus ocellatus, both of which spawn in spring, were investigated in a lowland river. Twenty nine freshwater mussels Unio douglasiae nipponensis (Unioninae) (63% of 46 individuals examined)hosted A. t. erythropterus eggs and embryos, mainly in their inner gills. One U. d.nipponensis (2.1%) and 2 Anodonta sp. (Anodontinae) (100%) hosted R. o. ocellatus eggs and embryos. The different mussel species utilized by the two bitterling may be important for their continued coexistence.
Two specimens of the diretmid fish Diretmoides veriginae Kotlyar,1987 (138-175 mm in standard length) were collected by bottom trawl (depth428-558 m) from the East China Sea, Japan. The species is characterized by the following combination of characters: postanal scutes present, spines absent on dorsal and anal fin bases, posterior ends of pectoral fins just reaching to above anal fin origin, total gill rakers 21-24. The specimens represent the first Japanese record and northernmost record of the species.
The winter distribution pattern of Japanese eight-barbel loach Lefua echigonia, in a controlled groundwater input conservation pond, varied with changes in input the position, the loach population showing aggregated dispersion. The distribution pattern, apparently dependent upon groundwater-inflow, was shown by multiple regression analysis to be strongly influenced by water temperature. Aggregation of the loach at groundwater-inflow sites that were warmer than elsewhere in the pond may indicate avoidance of low winter water temperatures, illustrating the importance of spring water for this loach in the winter season.
Ninety-nine synaphobranchid specimens, collected from Japanese waters between Hokkaido and Fukushima Prefectures, were identified as Ilyophisnigeli Shcherbachev and Sulak in Sulak and Shcherbachev, 1997 on the basis of the following combination of characters: body scaled; 5 or 6 supraorbital pores; 1or 2 frontal pores; 140-152 total vertebrae; 80-113 total lateral line pores, lateral line ending well anterior to tip of tail; and gill slits horizontal or slightly oblique. Originally described from nine specimens collected from the Pacific slope off Japan, the species, which has been overlooked by Japanese ichthyologists, is redescribed on the basis of the newly-collected specimens. A new standard Japanese name, “Yuki-hora-anago” is proposed for the species.