Matt Clarke looks at the freshwater Marbled Cambodian whipray, and explains why identifying members of this genus is so tricky.
Common name: Marbled Cambodian whipray
Scientific name: Himantura oxyrhyncha
Origin: The holotype of this species came from Saigon, Vietnam, with others in the type series being collected from Pnom Phen and the Mekong river system in Cambodia. However, new data mentioned in Deynat and Fermon (2001) says that the range extends to Thailand, Sumatra and Borneo.
Diet: Said to feed predominantly on aquatic invertebrates such as shrimps, and on small fishes. These can sometimes be hard to feed when first imported.
Size: This is one of the smallest Himantura, at a disc size of around 35cm/15". However, it has an enormously long tail (at least twice as long as the disc) and needs lots of free-swimming space.
Aquarium: A large, well-filtered aquarium with lots of free-swimming space is needed for this ray. Due to its large size, an extra wide tank is needed, ideally something like 150 x 90 x 60cm/5' x 3' x 2' would be a good minimum, preferably much bigger, though. As with other rays, a bare-bottom or a sandy substrate suits these fish best.
Water: Unlike some other members of the Himantura genus, this one, according to Deynat and Fermon (2001) is found in freshwater so don't add salt. Although the exact chemistry of the water doesn't appear critical, like their South American counterparts, Himantura rays are completely intolerant of pollution.
Identification: Himantura are not very easy to identify and most of the studies looking at them use radiography to count the number of vertebrae and radial cartilages, which are obviously invisible to us fishkeepers. The major snag with these rays is that the change in shape and colour pattern as they mature, making them very tricky to ID accurately. Most of the characters used to identify oxyrhyncha are beyond the fishkeeper and concern vertebrae, radials, jaw structure and tooth rows. See Deynat and Fermon (2001) for more details.
Similar species: This stingray is easily confused with H. uarnak and H. krempfi. Both have previously been confused by scientists and Deynat and Fermon's recent work on the species suggests the krempfi are actually just juvenile oxyrhyncha. Reticulated colouration is limited to a handful of Himantura including oxyrhyncha, krempfi, granulata and, in some specimens, uarnak.
Notes: These rays aren't related to the commonly sold South American ones. The neotropical rays are members of the family Potamotrygonidae, while these are in Dasyatidae, with a number of predominantly Indo Pacific species. The Himantura genus contains more than 22 species including: H. alcockii; bleekeri; chaophraya; draco; fai; fluviatilis; gerrardi; granulata; walga; imbricata; jenkinsii; krempfi; marginatus; microphthalma; granulata; uarnak; schmardae; signifer; toshi; uarnacoides and undulata. There is also one undescribed one, known as H. sp. A, which is a relative of both oxyrhyncha and uarnak.
Availability: These aren't regularly imported, possibly because many people believe them to be brackish, which admittedly some Himantura are. We spotted this one on sale at Wholesale Tropicals, London (0207 739 5356).
Price Expect to pay at least 100 for one of these.