Giant freshwater stingray (Himantura chaophraya)

Awe-inspiringly large, the giant freshwater stingray lives up to its name, possessing a venomous sting and a large whip-like tail ⁽²⁾. It is brown on the upper surface of its broad, thin, disc-shaped body, and paler beneath with a ring of black around the edge. It has a large snout but small eyes ⁽³⁾.

Size

Total length: up to 500 cm ⁽²⁾

Wing diameter: up to 240 cm ⁽²⁾

Maximum weight: 600 kg ⁽²⁾

Despite its enormous size, rivalling the Mekong giant catfish as largest freshwater fish in the world, the giant freshwater stingray is elusive and understudied. It is thought to mature at around 110 cm across and gives birth to live young of 30 cm across ⁽⁴⁾. It is venomous but uses its sting in self-defence as it preys upon invertebrates and relatively small fish ⁽²⁾.

Thought to occur in most large rivers of tropical Australia, as well as the Fly River basin, New Guinea, the Mahakam River basin, Borneo and several rivers in Thailand ⁽⁴⁾.

Inhabits the sandy bottoms of large rivers and estuaries ⁽¹⁾.

The giant freshwater stingray is classified as Vulnerable (VU A1bcde + 2ce) on the IUCN Red List ⁽¹⁾.

In 1992, Thai fisherman reported having caught 25 individuals, but the following year this figure fell to just three, hinting at a rapid decline ⁽⁴⁾. Threats in Thailand are from poor habitat management, including the destruction of the forest canopy which leads to drought upstream and flooding downstream during the monsoon, as well as dam building which prevents migratory fish breeding successfully, and therefore reduces available prey. In Australia the main threat to this species is thought to be silt from uranium mines which contains heavy metals and radio-isotopes. However, it is not known how threatening this is to these fish ⁽⁴⁾. Throughout its range, the giant freshwater stingray is at risk from both direct and incidental fishing, habitat destruction and range fragmentation leading to inbreeding depression ⁽²⁾.

Further research into this incredible fish’s biology and status is necessary. The Australian government plan to form a national recovery team who will attempt to compile information on the distribution, abundance and ecology of the giant freshwater stingray ⁽⁴⁾.

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the conservation of sharks and rays see:

• Save Our Seas Foundation:
  http://www.saveourseas.com
• Project Aware:
  http://www.projectaware.org/

Inbreeding depression

The reduction in viability, birth weight, and fertility that occurs in a population after one or more generations of inbreeding (interbreeding amongst close relatives).

Invertebrate

Animals with no backbone.

1. IUCN Red List (March, 2005)
   http://www.redlist.org
2. FishBase (March, 2005)
   http://64.95.130.5/Summary/SpeciesSummary.cfm?ID=11693&genusname=Himantura&speciesname=chaophraya
3. Monkolprasit, S. and Roberts, T.R. (1990) Himantura chaophraya, a new giant freshwater stingray from Thailand. Japanese Journal of Ichthyology, 37(3): 203 - 208.
4. Conservation overview and action plan for Australian threatened and potentially threatened marine and estuarine fishes (March, 2005)
   http://www.deh.gov.au/coasts/species/marine-fish/dasyatididae2.html