On the Population Status and Migration of Pangasiid Catfishes in Lancangjiang River Basin, China
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Abstract
Four species of Pangasiid catfishes were once recorded in China. In recent years, several important revisions have been made to the taxonomy of the family Pangassiidae by some ichthyologists. As a result of these revisions, the original taxonomic system has changed greatly; a total of 22 valid species belonging to three genera is now recognized in the world. Because Pangasiid fishes in China have not been revised according to the new system, it is unavoidable that some confusion is present in species description. Based on specimen examinations and records in China since 1960, the present paper reconfirms that there is a total of three species of pangasiid fishes in China: Pangasius sanitwongsei Smith, Pangasius djambal Bleeker, Pangasius micronema Bleeker. Based on all the data and specimens available, the population status and threatening factors have been analyzed. According to the data, all three species of pangasiid fishes are rare critically endangered in the lower Lancangjiang River. Three specimens of P. sanitwangsei were collected in 1959 and no more have been collected since. Aside from two specimens of P. djambal collected in 1959, one more specimen has been caught from Buyuanjiang at Menglun by an ichthyologist of the Institute of Hydrobiology. Pangasius micronema is slightly more common than the above two species. One specimen was collected from Buyuanjiang River at Menglun in 1959 and five individuals have been collected since from the reach of the Lancangjiang River between Ganlanba and Jinghong in 1966. One specimen of P. micronema was also collected from the reach of Jinghong in 1967 by the Yunnan Fishery School. The most recent three specimens were caught close to the join of Buyuanjiang River to Lancangjiang River in 1978. All specimens were collected around May and June, which is recognized as the breeding season of pangasiid fishes. This suggests that pangasiid fishes migrate to the lower Lancangjiang River mainly for breeding, rather than feeding. The occurrence of pangasiid fishes in Xishuangbanna was analyzed together with the discharge records of the Lancangjiang River in March and April in Jinghong. A high correlation was demonstrated between these two factors, with 81.3% of specimens caught in years when a high discharge appeared in March and April. A high discharge in March and April may be a signal of summer monsoon, prompting the pangasiids to begin their breeding migration towards the upper MekongLancangjiang River. Populations of the three pangasiid species have been declining since 1970. The decline is not correlated to dam construction because so far no dams have been constructed in the stem rivers of the lower Lancangjiang River. Threatening factors may include overfishing and damage from boat turbines. If any dams are planned to be built in the lower Lancangjiang River, the conservation of pangasiid fishes should be carefully considered. We strongly suggest setting up the Buyuanjiang River as a nature reserve for fishes and other aquatic organisms.
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