SBR- Content.pmd - INBO

State of the Basin Report - 2003Juvenile pangasiid catfishes have traditionally been capturedin fine meshed dai nets in the Mekong River in southernCambodia and northern Viet Nam for stocking in grow-outcages or ponds. Only 15 percent of this catch is kept; theother eighty five percent are killed and discarded in theseparation process. 113 These are the larvae of 160 non-targetspecies. Thus approximately 9 kg of non-target fish seedare killed for each kg of river catfish seed collected. Fearingthe damage done by this destructive fishing method, thecapture of wild pangasiid fry and fingerlings has beenprohibited in both Cambodia and in Viet Nam. 114 DespiteViet Nam producing more than 270 million river catfish fryby artificial propagation in 1999, fish farmers believe thatwild fish grow faster and prefer to buy wild fry, even if theyare more expensive. 115 As a result, the illegal collection ofriver catfish seed still continues, particularly in Cambodia. 116Introduction of exoticsExotics are generally introduced for aquaculture, forbiological pest control, and for the aquarium trade. The bighead carp (Hypophthalmichthys nobilis), silver carp(Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idellus), common carp (Cyprinuscarpio), rohu (Labeo rohita), catla (Catla catla), mrigal (Cirrhinus cirrhosus), tilapia (Oreochromissp.), and the African catfish (Clarias gariepinus), are now widely used for aquaculture in the fourLMB countries. Most of the above mentioned species have probably established breeding populationsin all or part of the basin. 117 It has further been reported that fishes introduced in the Mekong Basinin China are now appearing in Thailand. 118The guppy (Poecilia reticulata) and the mosquito fish (Gambusia affinis), originally introduced asornamentals and to control mosquitoes are now widespread in ditches and ricefields throughout thebasin. These same habitats have been colonised by the South American loricariid catfish (Hypostomusplecostomus), which is common in polluted water bodies. 119There is also a growing, but as yet unregulated, aquarium fish trade from Thailand to Singapore,and also from Lao PDR to Thailand and to Viet Nam. Fish species are also traded into the MekongBasin from outside the region. There are concerns that without appropriate management measures,trade in aquarium fish will negatively affect biodiversity in the near future. 120Risks from the uncontrolled introduction of exotic fish species include competition and displacementof indigenous fish species, reduced biodiversity, hybridisation, loss of genetic diversity and thepossible introduction of disease pathogens and parasites. 121PollutionFishing with explosives cost this StungTreng fisher the lower part ofhis right armPollution would become a major concern for the Mekong fishery if it formed a biological barrier tothe dispersion of fish eggs or the migration of fish larvae and adults. Pollution includes agriculturalrun-off (fertilisers, herbicides and pesticides); human sewage and storm water from urban areas;and industrial effluents. Point sources of pollution are currently not a major issue for the fisheriesof the LMB, although there have been instances of localised pollution which have been sufficientlysevere to cause fish kills. 122118