Outlook less bleak for Giant catfish

Wild populations of the world's largest catfish species might be more robust than previously believed, according to the results of a new genetic study.

The molecular analysis of the Giant Mekong catfish, Pangasius gigas, has shown that it is still genetically diverse, despite a considerable drop in the size of the wild population.

The species, which is currently classified as Critically Endangered on the IUCN Red List, is the subject of an ongoing captive-breeding programme aimed at replenishing wild stocks after decades in decline.

The new study, which has just been published in the journal Animal Conservation, examined the diversity of mitochondrial DNA in 672 specimens of Pangasius gigas and eight closely related species.

The results identified four haplotypes (closely linked genetic markers on a chromosome) in Pangasius gigas from just 16 samples taken from natural populations.

Haplotype diversity and nucleotide diversity ranged from 0.1180.101 to 0.6670.141 and from 0.00020.0003 to 0.00160.0013, respectively.

The authors believe that Pangasius gigas populations may be more genetically robust as a result:

"The results, in spite of the limited sample size for some species investigated, indicated that the level of genetic variation observed in wild populations of the Mekong giant catfish (haplotype diversity=0.3500.148, nucleotide diversity=0.00090.0008) is commensurate with that of some other related species.

"Present wild populations of this species carry a genetic signature of the historically larger populations."

Pangasius gigas, which is a member of the Siluriformes family Pangasiidae, is one of around 27 species in the genus Pangasius.

The fish was originally placed in a genus of its own, Pangasianodon, but was subsequently moved to Pangasius in recent studies.

For more information see the paper: Na-Nakorn, U., S Sukmanomon, M Nakajima, N Taniguchi, W Kamonrat, S Poompuang and TTT Nguyen (2006) - MtDNA diversity of the critically endangered Mekong giant catfish (Pangasianodon gigas Chevey, 1913) and closely related species: implications for conservation. Animal Conservation 9: 483-494.