| Co-Investigator(Kenkyū-buntansha) |
KAN Ting T. Senior Lecturer, University of Papua New Guinea, 水産学科, 上席講師
LAST Peter R. Researcher, Csiro Marine Laboratories, 水産研究部, 研究員
BABA Osamu Instructor, Tokyo University of Fisheries, 水産学部, 助手 (40189725)
MIZUE Kazuhiro Professor, Nagasaki Junior College, 教授 (40039706)
TANAKA Sho Associate Professor, Tokai University, 海洋学部, 助教授 (90138636)
OTAKE Tsuguo Research Associate, the University of Tokyo, 海洋研究所, 助手 (20160525)
SANO Mitsuhiko Instructor, the University of Tokyo, 農学部, 助手 (50178810)
OGAWA Kazuo Instructor, the University of Tokyo, 農学部, 助手 (20092174)
WATANABE Shugo Associate Professor, the University of Tokyo, 農学部, 助教授 (40111489)
TANIUCHI Toru Associate Professor, the University of Tokyo, 農学部, 助教授 (00012021)
|
|---|
| Research Abstract |
A total number of 67 elasmo branch specimens were collected from seven river systems in northern Australia and Papua New Guinea during investigations in 1989 and 1990. They comprised seven species, Carcharhinus leucas, Glyphis sp., Himantura chaophraya, Himantura uarnak, Pristis clavata, Pristis cuspidatus and Pristis microdon. Of these, P. clavata was captured in sea water entering a river. H. uarnak, P. cuspidatus, and a mature male P. microdon were obtained from an estuaty. P. mictrodon was collected from four river systems and C. leucas from three rivers. H. chaophraya was recorded in Australia for the first time. Glyphis sp. differed from a second undescribed Glyphis sp., occurring in Queensland.
A preliminary revision for the family Pristidae revealed two genera comprising six species in the world. However, electrophoretic analyses of freshwater elasmobranchs suggested that generic variation is very small within the species studied. Sexual dimorphism was found in the number of rostral teeth of Pristis microdon. Urea content, ionic concentrations of sodium, chloride, calcium and magnesium in marine P. clavata, were all twice as high as those in freshwater P. microdon. Osmolarity of freshwater elasmobranchs showed half of marine P. clavata, which in turn indicated higher osmolarity than marine sharks. Histological examination of the rectal glands of sawfish and sharks leads to the idea that these elasmobranchs remained in freshwater for short periods of time. Age and growth study using vertebral centra demonstrated that the annual growth rate for P. microdon was 18 cm in the first year and 10 cm in the tenth. Three species of ectoparasites were observed on the gills of P. microdon. Two species of monogeneans, Nonacotyle pristis, gen et sp. nov. and Pristochocotyle papuensis sp. nov. were described.
|
