Amazon river dolphin (Inia geoffrensis; boto

Japanese: アマゾンカワイルカ（英語表記）Inia geoffrensis; boto

The Amazon river dolphin is a member of the Amazon river dolphin family, suborder Odontoceti, and genus Pectini. Its body length is 2.3 to 2.8 meters, with males being larger than females. Males can reach a maximum weight of about 160 kg. Its birth length is about 80 cm. Its body color is gray to pink, becoming lighter from the back to the abdomen. Some whales are entirely pink. Young whales are blackish gray, but as they grow, the pink areas increase. It has one blowhole located on the midline of the head. Its beak is extremely long and slender, and sparsely covered with bristles. The forehead rises sharply from the base of the beak, and the head is small and round compared to the body. It has small eyes. Its dorsal fin is located in the posterior two-thirds of the body, low and long, gradually rising from the neck, and forming a keel (ridge-like protuberance) toward the caudal fin after passing the apex. The caudal fin is relatively large and wide. The pectoral fin is also very large and triangular with a slightly concave rear edge. The teeth are thick and arranged along the lips of the upper and lower jaws in 23 to 35 pairs on both sides. The teeth in front of the beak are conical, but the crowns of the teeth in the back are mushroom-shaped. They may live in groups of 12 to 15 individuals, but usually move alone or in groups of a few individuals. They move slowly, and only rise to the surface to expose their head and part of their dorsal fin above the water. In Brazil, the peak birth season is during the rainy season from May to July. They prey on various types of fish near the river bottom, and when they eat large prey, they tear them into suitable pieces and swallow them. They sometimes catch prey with pygmy dolphins. They are widely distributed in the Amazon and Orinoco river basins, and in the rainy season they enter not only the main river but also tributaries and lakes. 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アマゾンカワイルカ科アマゾンカワイルカ属。体長は 2.3～2.8mで，雄は雌より大きい。雄の最大体重は約 160kgに達する。出生体長は約 80cm。体色は灰色から桃色で，背部から腹部に向ってより淡色となる。全身桃色を呈するものもある。幼鯨は黒灰色であるが，成長に伴い桃色の部分が増す。噴気孔は1個で頭部正中線上にある。嘴 (くちばし) はきわめて細長く，剛毛がまばらに生える。嘴のつけ根から前頭部が急に盛上がり，頭部は体に比して小さく丸い。眼は小さい。背鰭 (せびれ) は体の後方3分の2に位置し，低く長く，頸部から次第に隆起し，頂点を過ぎると尾鰭に向ってキール (稜状の隆起) を形成する。尾鰭は比較的大きく幅が広い。胸鰭もきわめて大きく三角形状をなし後縁がややくぼむ。歯は太く上下顎骨の口唇に沿って左右 23～35対並び，嘴前方の歯は円錐歯であるが，後方の歯は歯冠部がキノコの傘状を呈する。 12～15頭の群れをなすこともあるが，通常は単独ないし数頭の群れで行動する。動きが緩慢で，頭部と背鰭の一部を水上に出す程度しか浮上しない。ブラジルでは5～7月の雨季に出産の最盛期を迎える。川底近くのさまざまな種類の魚類を捕食し，大型の餌を食べるときは適当な大きさに裂いて飲みこむ。またコビトイルカとともに餌を捕ることがある。アマゾン川およびオリノコ川流域に広く分布し，雨季には本流だけでなく支流や湖にも進入する。絶滅危惧種。

出典　ブリタニカ国際大百科事典小項目事典ブリタニカ国際大百科事典小項目事典について　情報

<<: "Amazon River Naturalist" - Amazon River Naturalist

>>: Amazon Development Agency - Amazon Development Agency