Fish Assemblage at the Lhalu Wetland:Does the Native Fish Still Exist
Non-native invasive fishes have been shown to be highly dangerous to aquatic ecosystems,and have caused huge ecological and economic costs.The Lhalu wetland,one of the most important wetlands in the Lhasa River basin,Tibet,China,represents the highest and largest urban wetland in the world.The ecosystem of the wetland was intensively disturbed by human activities before it was listed as a national reserve in 2005.Although 2 exotic fishes(Carassius auratus(Linnaeus) and Monopterus albus(Zuiew)) were found in the wetland in a survey which was carried out from 2001 to 2003,unfortunately they did not receive enough attention they deserve.In order to examine whether the native fish still exists,the fishes were studied by gillnets and setting nets in April and June in 2010 and April in 2011.Of the 12 species collected,C.auratus(Linnaeus),Cyprinus caupio Linnaeus,Ctenopharyngodon idellus(Cuvier et Valenciennes),Pseudorasbora parva(Temminck et Schlegel),Misgurnus anguillicaudatus(Cantor),Silurus asotus Linnaeus,and Hypseleotris swinhonis(Gunther) were alien species,and Oxygymnocypris stewartii(Lloyd),Schizopygopsis younghusbandi younghusbandi Regan,Triplophysa stewartii(Hora),T.stenura(Herzenstein) and T.tibetana(Regan) were native species.The non-native fish P.parva and C.auratus were the dominant species,as the former took up 83.9 % of the total fish abundance performed by setting nets and the latter accounted for 93.0 % of that performed by gillnets.Both of them had a wide distribution,almost spreading all over the wetland.By contrast,all the 5 native species were rare,with poor abundance( 2% by number) and low occurrence.Non-native C.carpio,C.idellus,M.anguillicaudatus,S.asotus and H.swinhonis were found at low density and low occurrence.For the unevenness of abundance among species,the fish assemblage had little diversity,as the value of the Shannon-Weiner index,Simpson index and Pielou's evenness index of fish assemblage sampled by gillnets were 0.343,0.866,and 0.213,respectively.Those indexes of fish assemblage sampled by setting nets were 0.638,0.855,and 0.290 respectively.This study demonstrates that although 5 native fishes still exist,the Lhalu wetland has been thoroughly invaded by non-native fishes,and no longer supported a distinct fish assemblage.It is suggested that restoring the water quality of the wetland,enhancing training and education for local people on the dangerousness of non-native fishes and eradication of non-native fishes are important to the conservation of fish fauna and ecosystems of the Lhalu wetland.