Which of the following is not a bird ?

Golden Mahseer is a large species of freshwater fish found in the Himalayan rivers, often referred to as the "tiger of the water," rather than a bird. While options like the Indian Nightjar or Spoonbill might sound unfamiliar to some, they are well-documented avian species found across the Indian subcontinent. The core concept being tested is the basic classification and identification of prominent Indian fauna and their respective habitats.