Habitat use by newly emerged fry of red-spotted masu salmon ( Oncorhynchus masou ishikawae ) in a mountain stream , northeastern Kyushu , southern Japan

Artificial fertilization experiments were performed and male and female gonads observed histologically to confirm the oldest known description (published 1934) of the reproductive mode for internal gamete association (IGA) in Vellitor centropomus (Cottidae). Stripped eggs from mature females were unfertilized such commencing after their immersion in seawater, indicating that V. centropomus is an IGA species. Many spermatozoa were stored in the immature ovary with non-vitellogenic oocytes, evidence that males of the species mature before females and that copulation occurs when females are still immature. The male reproductive organ consisted of paired testes, a specialized seminal vesicle and a functional urogenital papilla. A sperm duct in the testicular hilus was absent. Spermatogenesis occurred sequentially, posterior most first, suggesting that it occurs over an extended period of time. A ventral luminal ampulla, central expanded main sperm duct and dorsal saccular ampulla were observed in the seminal vesicle, all parts being involved in sperm storage. The saccular ampulla had an exocrine function, secreting a periodic acid–Schiff (PAS)-positive substance. Sperm heads stored in the posterior part of the testis or lumen of the seminal vesicle were also PAS-positive. Sperm heads were slender, a typical morphology in IGA species. (Corresponding author: Yasunori Koya, Department of Biology, Faculty of Education, Gifu University, Yanagido, Gifu, Gifu 501–1193, Japan; e-mail: koya@gifu-u.ac.jp) Japanese Journal of Ichthyology Vol. 62, No. 2, pp. 133–147 Feeding behavior and interactions of three cyprinid species in experimental streams Hiromu Ogawa and Osamu Katano Abstract Three cyprinid fishes, pale chub Zacco platypus, dark chub Nipponocypris temminckii and Japanese dace Tribolodon hakonensis, are common in the middle reaches of Japanese rivers. To investigate their feeding behavior, and intraand interspecific interactions, 10 individuals each of pale chub, pale chub and dark chub, pale chub and Japanese dace, and dark chub and Japanese dace, respectively, were observed in four experimental ponds that simulated natural rivers. All species exhibited intraand interspecific aggressive behavior, pale chub and dark chub establishing intraspecific dominance hierarchies. Large individuals tended to win in interactions, although dark chub, the most aggressive among the three species, occasionally won against large pale chub and Japanese dace. Pale chub, dark chub and Japanese dace most frequently exhibited algal feeding, drift feeding and bottom feeding, respectively. However, marked individual differences existed in feeding behavior and appearance rate. Habitat use by the three species did not differ greatly, but in the pond inhabited by dark chub and Japanese dace, the former showed the more concentrated habitat use. Feeding behavior of pale chub was affected by dark chub and growth rate of pale chub was lowered in the presence of Japanese dace. The behavior of the three cyprinid species was partly species-specific, but was also affected by individual differences and the presence of other species. (Corresponding author: Hiromu Ogawa; Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Minato Tokyo 108– 8477, Japan; e-mail: hiromu0725@fra.affrc.go.jp) Japanese Journal of Ichthyology Vol. 62, No. 2, pp. 149–156 Intergeneric hybridization between Japanese char and red-spotted masu salmon in a tributary of the Ibigawa River, Gifu Prefecture, Japan Takahiko Mukai, Ryo Futamura, Taiki Niwa, Akihiko Goto, Naoki Miwa, Wataru Ishizuka, Yuichi Yaoi and Masaki Takagi Abstract Japanese char Salvelinus leucomaenis, red-spotted masu salmon Oncorhynchus masou ishikawae, hybrid individuals were collected from a tributary of the Ibigawa River, Gifu Prefecture, Japan. The char and hybrids were mainly distributed in the headwater area where eyed eggs of red-spotted masu salmon are released in each year. Principal component analysis (PCA) of the morphological features of parental and hybrid individuals indicated that hybrid body shape was similar to that of char. Partial nucleotide sequences of mitochondrial DNA indicated the female parental species to be red-spotted masu salmon, without exception. Genotyping of three loci of short interspersed repetitive elements (SINE) of inserted alleles showed all hybrid individuals to be F1, with no evidence of backcrossing. These results indicated that the introduced red-spotted masu salmon hybridized with male char, with a high survival rate of sterile F1 offspring. (Corresponding author: Takahiko Mukai, Faculty of Regional Studies, Gifu University, 1– 1 Yanagido, Gifu, 501–1193, Japan; e-mail: tmukai@gifu-u.ac.jp)