Transparent-Scaled Variant of the Rosy Bitterling, Rhodeus ocellatus ocellatus (Teleostei: Cyprinidae)

Production of Chinese rosy bitterling offspring derived from frozen and vitrified whole testis by spermatogonial transplantation

Bitterling is a small cyprinid fish facing an increasing risk of extinction owing to habitat destruction and decreasing freshwater mussel population that are used as their spawning substrates. Owing to their large size and high yolk contents, methods for cryopreservation of their eggs or embryos, which is a promising method for long-term preservation of their genetic resources, are still not available. We conducted this study to evaluate the feasibility of gamete production by transplanting cryopreserved testicular cells into germ cell-less recipients that were produced by knockdown of dead end gene. Immature testes isolated from recessive albino Chinese rosy bitterlings were cryopreserved by slow freezing or vitrification. Approximately 3000 slow-frozen or vitrified cells were transplanted into the peritoneal cavity of 4-day-old germ cell-less wild-type Chinese rosy bitterlings. We observed no significant differences in the incorporation rates of the slow-frozen and vitrified cells into the genital ridges of recipients compared with those of freshly prepared cells. When the recipients matured, almost half of the male or female recipients that received freshly prepared, slow-frozen, or vitrified cells produced gametes derived from donor cells, with no significant differences in their fecundity among the 3 groups. Moreover, fertilization of the resulting eggs and sperm produced donor-derived offspring exhibiting the albino phenotype. Therefore, the abovementioned methods could be used as a powerful and practical method for long-term preservation of bitterling genetic resources for biotic conservation.

The reproductive ecology of the southern red tabira bitterling Acheilognathus tabira jordani in Japan

The life history, population and reproductive variables of the southern red tabira bitterling Acheilognathus tabira jordani were investigated in a lowland reach of the River Ohara in Shimane Prefecture, western Honshu, Japan. Acheilognathus t. jordani, like all other species of bitterling, lays its eggs on the gills of freshwater mussels. It was the only species of bitterling present in the study reach, and three species of bivalve mussel were available to it for spawning: Anemina arcaeformis, Anodonta lauta and Corbicula leana. Spawning by A.t. jordani was recorded between early April and early July in 2003 and began at a size of 38. 0 mm standard length (L(S)) in the 1+ age class. Ovipositor length (L(OP)) during oviposition was positively correlated with female L(S), and showed significant seasonal variation, with a mean +/-s.d.L(OP) of 27. 5 +/- 5. 3 mm ranging from 16. 8 to 42. 0 mm during the spawning period, which was shorter than that of a previously studied A. t. tabira population. Eggs of this subspecies are relatively long and elliptic in shape, with a volume of c. 2. 4 mm(3). Egg number correlated positively with female L(S) and both egg shape and volume changed significantly with season. The population size of adults was estimated to be 850 individuals, and comprised age 0+ to 3+ individuals with L(S) ranging from 12. 0 to 72. 2 mm. The population sex ratio was significantly female biased, with seven females: three males. Egg shape and size and L(OP) during oviposition in the present A. tabira population may be the result of local adaptations to the mussel species utilized and no competition with other bitterling species for spawning sites.

Modes of reproduction of the hybridogenetic fish Squalius alburnoides in the Tejo and Guadiana rivers: An approach with microsatellites

The Squalius alburnoides complex was produced by hybridization between female S. pyrenaicus (PP genome) and an hypothetical paternal ancestor related with Anaecypris hispanica (AA genome). This study examined a diversity of mating types and found that there is the potential for considerable gene exchange among diploid, triploid and tetraploid hybrids. Using microsatellites, genomes were attributed to Squalius pyrenaicus (P) or reconstituted "nuclear non-hybrid"S. alburnoides (A), and subsequently confirmed in hybrids. Recombination of AA genomes in the "nuclear non-hybrid males" and recombination of the homogametic genomes (AA or PP) after exclusion of the heterogametic genome in triploid females (PAA) were observed by analysing parents and progeny of breeding experiments. Reproduction of tetraploids, generating a symmetric tetraploid genotype (PPAA) in the progeny, suggests a process that could potentially lead to the formation of a new bisexual species. Present results also support: (i) previously hypothesized pathways, in which PPA S. alburnoides females exclude the A genome, exhibit meiotic recombination between the P genomes and generate haploid eggs; (ii) reconstitution of the diploid maternal ancestor genome (PP) as well as of the unknown paternal ancestor (AA); (iii) the occurrence of the same genomic reproductive mechanisms when Anaecypris hispanica is involved; and (iv) the existence of an A. hispanica-like ancestor as the paternal ancestor of S. alburnoides.

Low Genetic Variation and Inbreeding Depression in Small Isolated Populations of the Japanese Rosy Bitterling, Rhodeus ocellatus kurumeus

The Japanese rosy bitterling, Rhodeus ocellatus kurumeus, has been affected not only by the invasion of another subspecies, R. o. ocellatus, from China, but also by habitat fragmentation. In this study, the effects of habitat fragmentation on the fitness of R. o. kurumeus were investigated. Owing to exclusion by R. o. ocellatus, R. o. kurumeus in Honshu and Shikoku has disappeared entirely, except for small populations in isolated man-made ponds in Osaka and Kagawa. In Kyushu it still occupies open water systems, into which R. o. ocellatus has only recently invaded. Meristic and genetic data show that the diversity of R. o. kurumeus is significantly lower in the isolated Osaka and Kagawa populations than the non-isolated Fukuoka population. The Osaka population is inferior to the Fukuoka population in terms of viability and growth. The viability of reciprocal inter-population hybrids between the Osaka and Fukuoka populations was, however, as high as that of the Fukuoka population. In addition to the high scores of band sharing index (BSI) in RAPD-PCR analysis, acceptance of transplanted scales among individuals, irrespective of natal pond, indicates that the Osaka population forms a highly inbred line. These results suggest that low genetic variation is associated with inbreeding depression in the small isolated Osaka populations. Consequently, the management of ponds, including the free movement of individuals, in addition to measures to prevent the invasion of R. o. ocellatus, is necessary for the conservation of R. o. kurumeus.