Adaptability and Conservation of Freshwater Elasmobranchs

1997 Fiscal Year Final Research Report Summary

• Project/Area Number: 08041156
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Field Research
• Research Field: General fisheries
• Research Institution: Tokai University
• Principal Investigator: TANAK Sho Tokai University. School of Marine Science and Technology, Professor, 海洋学部, 教授 (90138636)
• Co-Investigator(Kenkyū-buntansha): MURAKAMI Masahiro University of Tokyo. Graduate School of Agricultural and Life Sciences. Associate Professor, 大学院・農学生命科学研究科, 助教授 (70134517) ; WATABE Shugo University of Tokyo. Graduate School of Agricultural and Life Sciences, Professor, 大学院・農学生命科学研究科, 教授 (40111489) ; TANIUCHI Toru University of Tokyo. Graduate School of Agricultural and Life Sciences, Professor, 大学院・農学生命科学研究科, 教授 (00012021) ; WONGRAT Prachit Kasetsart University. Faculty of Fisheries, Assistant Professor, Faculty of Fisheries, 講師 ; OTAKE Tsuguo Mie University. Faculty of Biological Resources, Associate Professor, 生産資源学部, 助教授 (20160525)
• Project Period (FY): 1996 – 1997
• Keywords: FRESHWATER STINGRAYS / MEKONG RIVER / CHAOPPHRAYA RIVER / GANGES RIVER / PHYLONGENETIC SYSTEMATICS / ADAPTABILITY FOR FRESHWATER / OSMOLITES / AGE AND GROWTH

Research Abstract

1) Eight species of freshwater stingrays were collected in Thailand and Laos : Himantura signifer and H. chaophraya from the Chao Phraya River ; H. gerrardii, H. bleekeri and unidentified Himnantura sp., from the Nan River ; Dasyatis laosensis from the Mekong River ; H krempfi and Pastinachus sephen from the Banpakong River.
2) Four species of freshwater stingrays were collected from the Ganges River System : Himanantura bleekeri H. gerrardii and Pastinachus sephen.
3) The molecular phylogenetic analyses by the parsimony and neighbor-joining methods based on DNA nucleotide sequences of the cytochrome b gene showed the general topology of the trees remained mostly unaltered. While species belonging to the genus Himantura formed one group, Dasyatis laosensis and Dasyatis sp. From Thailand formed the other group. The data failed to show clear phylogenetic relationships of the genus Pastlhachus with the genera Dasyatis and Himantura.
4) Analytical data of blood serum composition, rectal gland weight / body weight ratio, and rectal gland morphology in freshwater stingrays suggested that each species did not fully adapt for freshwater environment. Statoconium Sr : Ca ratios of freshwater stingrays were much lower than those of the stingrays from estuary and sea. The ratio might represent the integrated environmental history of individual freshwater stingrays.
5) Analysis of the free amino acids contents in the muscles of freshwater and brakish stingrays indicated that Tau and Urea play an important role as organic osmolites.
6) Himantura signifer is the most common freshwater stingray in Thailand. The male seems to be mature between 210 and 230 mmDW, while the female is between 250 and 260 mmDW. Mostly species become mature by 5 years old, though the giant species, Himantura chaophraya, did not attain to mature at 7 years old.