Ganges River dolphin (English spelling) Platanista gangetica; Ganges River dolphin

Japanese: ガンジスカワイルカ（英語表記）Platanista gangetica; Ganges River dolphin

The Ganges River dolphin belongs to the genus Ganges River dolphin, and is part of the order Cetacea, suborder Odontoceti, family Pectiniidae, genus Pectiniidae. Males can reach a body length of about 2.2 m, and females about 2.6 m. They can weigh up to 108 kg. Their birth length is 65-90 cm. Their body color is gray, with a slightly darker back. They have one blowhole, located to the left of the midline of the head. Their eyes are sunken and very small. Their neck is clearly positioned because their cervical vertebrae are long and free. Their dorsal fin is located three-fifths of the back of their body, only slightly raised, wide, triangular, and has a very blunt tip. On their back, they have a keel (ridge-like protuberance) from the dorsal fin to the center of the caudal fin, and on their ventral side, they have a keel slightly behind the anus. Their pectoral fin is nearly square, broad, and relatively large. Their beak is very thin and long. There are 26-39 pairs of thin conical teeth on the upper jaw and 26-35 pairs on the lower jaw. The teeth in front of the beak are long and stick out even when the mouth is closed, and are similar in shape to those of a gharial (a fish-eating crocodile). They usually live in small groups of less than 10 individuals, and are particularly likely to live in groups of one or two. They breed throughout the year, but are most active from December to January and March to May. They use one side of their pectoral fin on the river bottom to use echolocation (echo detection) to avoid obstacles and find food. They mainly prey on fish. They are widely distributed in the Ganges, Brahmaputra, and Karnaphuli river basins. An endangered species.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

クジラ目ハクジラ亜目ガンジスカワイルカ科ガンジスカワイルカ属。体長は雄約 2.2m，雌約 2.6mになる。体重は約 108kgに達する。出生体長は 65～90cm。体色は灰色で，背部はやや濃色である。噴気孔は1個で頭部正中線の左側に位置する。眼は陥没していてきわめて小さい。頸椎骨が長く遊離しているので，頸部の位置が明瞭である。背鰭 (せびれ) は体の後方の5分の3に位置し，わずかに隆起する程度で，幅が広く三角形状で先端はきわめて鈍い。背部には背鰭から尾鰭中央にかけてキール (稜状の隆起) があり，腹側には肛門やや後方にキールがある。胸鰭は四角形に近く，幅広で比較的大きい。嘴 (くちばし) はきわめて細く長い。細い円錐歯が上顎骨に左右 26～39対，下顎骨に左右 26～35対ある。嘴前方の歯は長く，口を閉じた状態でも外に出ていて，形状はガビアル (魚食性のワニ) に似ている。通常 10頭以下の小群で行動し，特に1～2頭で行動することが多い。繁殖期は周年であるが，なかでも 12月～1月，3～5月が盛んである。胸鰭の片側を川底につけてエコロケーション (反響探査) を行い，障害物を避けたり，餌を探したりする。おもに魚類を捕食する。ガンジス川，ブラマプトラ川，カルナプリ川流域に広く分布する。絶滅危惧種。

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