Reproductive capacity was investigated in naturally occurring triploid individuals of the loach Misgurnus anguillicaudatus collected from Memanbetsu Town, Abashiri County, Hokkaido Island, Japan. These triploids have been considered to appear by accidental incorporation of the haploid sperm genome from normal diploid into unreduced diploid eggs from the clonal lineage that usually reproduces unisexually. By fertilization with sperm from the normal male, one triploid female gave many inviable aneuploid (2.1-2.7n) and very few tetraploid progeny, whereas the other produced both diploid and triploid progeny. The results suggest that at least four different types of eggs can be formed in triploid females in this locality. In contrast, no progeny hatched when eggs of the normal female were fertilized with sperm or sperm-like cells obtained from triploid males. These gametes exhibited inactive or no motility after adding ambient water. They had larger head sizes than those of normal haploid sperm and had a short or no tail. Although their ploidy was triploid or hexaploid, a small number of haploid cells were detected in the semen by flow cytometry. Thus, triploid males were generally sterile, but they have a little potential for producing very few haploid sperm.

The loach Misgurnus anguillicaudatus comprises diploid, triploid and diploid-triploid mosaic individuals in a wild population of the Hokkaido island, Japan. Previous studies revealed the presence of a cryptic clonal lineage among diploid loaches, which is maintained by uniparental reproduction of genetically identical diploid eggs. In the present study, we analyzed distribution and genetic status of diploid and triploid cells in infrequent mosaic males. Flow cytometry, microsatellite genotyping and DNA fingerprinting verified that mosaic males consisted of diploid cells with genotypes identical to the natural clone and triploid cells with diploid genomes of the clonal lineage plus haploid genome from sperm nucleus of the father. Thus, the occurrence of diploid-triploid mosaicism might be caused by accidental fertilization of a diploid blastomere nucleus with haploid sperm after the initiation of clonal development of unreduced eggs. Such mosaic males produced fertile sperm with diploid DNA content. The experimental cross between normal diploid female and diploid-triploid mosaic male gave rise to the appearance of triploid progeny which exhibited two microsatellite alleles identical to the clonal genotype and one allele derived from the normal female. In DNA fingerprinting, such triploid progeny gave not only all the DNA fragments from the clone, but also other fragments from the normal female. Induced androgenesis using UV irradiated eggs and sperm of the mosaic male gave rise to the occurrence of diploid individuals with paternally derived microsatellite genotypes and DNA fingerprints, absolutely identical to the natural clonal lineage. These results conclude that the diploid-triploid mosaic male produced unreduced diploid sperm with genetically identical genotypes. The spermatogenesis in the clonal diploid cells under the mosaic condition suggests that triploid male somatic cells might transform genetically all-female germ cells to differentiate into functionally male gametes. The discovery of the mosaic male producing unreduced sperm suggests the theoretical occurrence of triploids and other polyploids by the syngamy of such paternally derived diploid gametes.

25Tetraploid fish, which are considered as key resources of diploid gametes for further breeding 26 and ploidy manipulation, can be artificially induced by inhibition of the mitotic cell division 27 with hydrostatic pressure or temperature treatments. Although many attempts have been 28 made to induce artificial tetraploid strains, successful establishment of viable and fertile 29 tetraploid strains are rare. In pond loach, Misgurnus anguillicaudatus, natural tetraploid 30 individuals are distributed in wild populations and diploid gametes from the tetraploid fish 31 have been used for various kinds of ploidy manipulation, but artificially induced tetraploid 32 strains have not been established yet. In the present study, we optimized starting timing of 33 the heat-shock treatment (41°C for 2 min) to inhibit a mitotic cell division in fertilized eggs of 34 the normal diploid pond loach between 21 and 51 min after insemination at 20°C incubation 35 temperature. After the treatment, we observed external appearance of hatching larvae and 36 flow-cytometrically determined ploidy status of the resultant larvae. Although tetraploid 37 and diploid/tetraploid larvae were obtained, the treating timings inducing these progeny 38 varied among crosses. Various kinds of ploidy such as haploidy, diploidy, triploidy, 39 pentaploidy, hexaploidy, aneuploidy and mosaic were detected in non-optimum heat-shock 40 timings for tetraploidization. Survivors, a tetraploid and a diploid/tetraploid mosaic male, 41 matured at the age of one year old, but they produced functional haploid spermatozoa. 42

The surface of concrete structures is subject to abrasion when they are constructed in sea water where ice movement is active. Abrasion occurs due to the friction force between ice sheets and the structure caused by the ice force working on the structure.Over the past ten years we have been conducting experiments with many types of concrete and their possible coating materials to find their characteristics of abrasion due to movements of ice sheets. In this experiment we calculated the abrasion rates (average amount of abrasion per 1 km movement of ice sheets) of various kinds of stone needed to estimate the abrasion amount due to movements of ice sheets which contain sand particles or not, and we also clarified the mechanism of abrasion.

Ice sheets in rivers, lakes, lagoons, port in cold regions are used for a variety of purposes. They are used as tracks on the ice, as roads for automobiles, as runways for airplanes, and as footholds for the construction of structures. Knowledge of physical and dynamic characteristics of natural ice sheets and techniques to estimate the hearing capacity of natural ice sheets against vertical loads are required to safety in using ice sheets. In this study, the authors indicate the theoretical