Two leading experts on Asian fishes have described a second species from the Silver shark genus Balantiocheilos.
Maurice Kottelat and Heok Hee Ng of the National University of Singapore named the new species as Balantiocheilos ambusticauda in a paper in the latest issue of the systematics journal Zootaxa.
Balantiocheilos ambusticauda was discovered from the Mekong and Chao Phraya drainages of Indochina - mainland Southeast Asia).
The Balantiocheilos genus was previously considered to be monotypic, with just a single species, the Silver shark, Balantiocheilos melanopterus.
However, a detailed comparison between Indochinese and Sundaic specimens previously believed to be B. melanopterus has shown that two distinct species can be recognised.
Balantiocheilos ambusticaudaThe species from Indochina is a new fish, named ambusticauda, which can be told apart from melanopterus by its shorter snout (27.5-33.9% of head length, compared to 33.2-39.1% of head length in melanopterus), narrower black margins on the pelvic and anal fins (distal third or less, compared to distal half or more on melanopterus), a a posteriorly directed groove at the rictus, versus straight in melanopterus.
Ng and Kottelat also believe that there might be some colour differences between the two species, but have not been able to confirm this themselves:
"Besides the differences in fin color, the live coloration of B. ambusticauda also appears to differ slightly from that of B. melanopterus.
"A photograph of live B. ambusticauda appearing in a Thai children's magazine circa 1970 shows some golden color on the dorsal surfaces of the head and body (C. Vidthayanon, pers. comm.), and there are unsubstantiated reports that the fish is an overall golden color (B. melanopterus in contrast
is an overall silver color in life and does not show any evidence of a gold color on the body in life)."
It's also believed to reach a slightly smaller size of 20cm/10", rather than the 35cm/14" sometimes seen in large B.melanopterus.
Believed extinctNg and Kottelat believe that the new species may already be extinct.
Humphrey and Bain (1990) have suggested that this is due to excessive collecting for the ornamental fish trade, however, Ng and Kottelat said there was no evidence to support this claim.
They said that by 1980, fisheries biologists in Thailand believed the fish had been wiped out in the wild, but all Balantiocheilos exported at that time were being captive-bred from fish of Indonesia origin.
The authors believe that the Silver shark, B.melanopterus, has also severely declined or disappeared in recent years. Forest fire pollution and the ornamental fish trade were cited as possible causes of the decline.
The species appears to have gone extinct in the Batang Hiri basin in Sumatra, and all species exported from Indonesia are now captive-bred according to recent studies.
The name ambusticauda means burnt tail, and refers to the black edges of the fins.
For more information see the paper: Ng HH and M Kottelat (2007) - Balantiocheilos ambusticauda, a new and possibly extinct species of cyprinid fish from Indochina (Cypriniformes: Cyprinidae). Zootaxa 1463: 13-20.