March 7, 2011 : Giant Freshwater Stingray

Giant Freshwater Stingray

The giant freshwater stingray (Himantura chaophraya) is a species of stingray in the family Dasyatidae, native to large rivers and estuaries of Southeast Asia. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500–600 kg (1,100–1,300 lbs). Its numbers are dwindling due to overfishing and habitat loss, and some local populations are in danger of going extinct. The smaller freshwater whipray of New Guinea and northern Australia was once considered to be conspecific with the giant freshwater stingray but is now recognized as a separate species.

Originally described from Thailand (where it occurs in the Chao Phraya, Nan, Mekong, Bongpakong, Tachin and Tapi Rivers), the giant freshwater stingray is also found in Indonesia (the Mahakam River Basin in Kalimantan) and Malaysia (the Kinabatangan River in Sabah). The rays across these different regions are likely to be isolated from each other, and it is yet unclear whether they represent populations of the same species or a species complex. It prefers a sandy habitat.

The giant freshwater stingray has a relatively thin, more or less oval-shaped pectoral fin disk and minute eyes. The snout is very broad with a projecting triangular tip. The mouth is small, with 4–7 papillae (2–4 large central and 1–4 small lateral) on the floor. The whip-like tail measures 1.8–2.5 times the length of the disk and lacks fin folds. The serrated spine on the tail is the largest of any stingray, reaching 38 cm (15 in) long. It is covered with a sheath of toxic mucus and is capable of piercing bone.

The upper surface of the body and tail are covered with small, rough tubercles, becoming sharp on the tail beyond the spine. The back is uniform brown to gray in color, sometimes becoming lighter towards the margins. The underside is white, with a distinctive broad, black band edged with small spots around the margins of the pectoral and pelvic fins. The tail is black past the spine. This species reaches at least 4.6 meters (15 ft) long and 1.9 meters (6.2 ft) across.