Three species have been described within the genus: Probarbus jullieni, Probarbus labeamajor and Probarbus labeaminor (Roberts 1992). All three are included in the IUCN List of Endangered Animals, the first as "Endangered", and the latter two as "Data deficient". In addition, Probarbus jullieni is listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), Appendix I.

Probarbus jullieni and Probarbus labeamajor appear to have very similar migratory habits, and although fishermen at many places can distinguish between the two species (e.g., they have different local names), they are reported to migrate together. A third species (Probarbus labeaminor?) was reported at Sungkom district, Nong Khai province (Thailand) with similar migratory habits to Probarbus jullieni and Probarbus labeamajor. Since the two first species appear to be very similar with respect to migratory habits, they are considered together in this publication.

The two species occur throughout the survey area, from the Mekong delta to the border between the Lao PDR, Thailand and Myanmar. As with most of the other migrating species covered by the current survey, the migrations of Probarbus can be divided into spawning migrations and trophic migrations.

Upstream spawning migrations occur between October and February from Kompong Cham (Cambodia) to the northernmost station of Chiang Khong (Thailand). Above the Khone Falls, the main spawning period was reported to be January to February, sometimes extending into March-April. At Chiang Khong, fishermen reported that Probarbus migrates up the Nam Ta tributary in the Lao PDR to spawn during March-April. A spawning site was described.

At Loei (Thailand), a site named Bung Ghang was reported to be a spawning ground. At Mukdahan (Thailand), spawning was reported at two Mekong sites named Don Son Korn and Don Nang Nean (the fisherman reported observing "a hundred fish gathering there"). Another fisherman at Mukdahan reported mature male fish with milt and seeing fish swimming near the surface during October-November.

In Sungkom district, Nong Khai province, three Probarbus species were reported to migrate together but spawn separately during January-February. Early-stage eggs were observed during October-November.

At Paksan (Lao PDR), ripe females were reported in March-April.

However, a report from Pak Lay, Xayabouri province in the Lao PDR, did not adhere to the information given in the other spawning reports. The report noted that eggs were observed in August, but the development stage of the observed eggs was not described. Further investigation is therefore needed to verify that observation.

There were no reports on actual spawning sites below the Khone Falls. Furthermore, reports on the occurrence of eggs in that stretch were less clear compared to reports from above the Khone Falls. Four reports, covering the stretch from Thalabovirrat near the Khone Falls to Sambor, stated that eggs were observed from November to March. However, at four stations from Sambor to Kandal, eggs were reported to occur from May to August, at a time when the fish were reported to migrate downstream. Since the development stages of the eggs were not mentioned, they could have been in a very early stage of development. The information could also indicate the presence of a different population (or even species) from further upstream. Further investigations are therefore needed for verification.

There were no reports on spawning or occurrence of eggs in the Mekong delta. In the delta, Probarbus sp. occur mainly as juveniles up to 40 cm. Only one station, Hong Ngu in Dong Thap province, reported fish of up to 90 cm.

Spawning of Probarbus has been quite well documented in previous studies. Roberts and Warren (1994) described the upstream spawning migration at the Khone Falls from October to January. They also reported that P. jullieni and P. labeamajor migrated together. A spawning site near Don Hee was identified.

Baird (1998) documented the Probarbus fisheries from October to January at Ban Hang Khone, just below the Khone Falls. Virtually all Probarbus spp. caught were in reproductive condition. The main species was Probarbus jullieni accounting for more than 65 per cent of the catch during that period, with Probarbus labeamajor accounting for just over 12 per cent.

Viravong (1996) documented a spawning ground in the Ou River in northern Lao PDR, and described in detail the spawning behaviour of Probarbus jullieni, during February 1995.

Finally, a Probarbus spawning ground in the Nam Lik River, in the Nam Ngum River catchment area, was documented during phase I of the present survey (Trial Survey) in 1998.

Trophic migrations were reported throughout the occurrence range. They occur mainly at the onset of the flood season and are mainly undertaken by juveniles and sub-adults. At a station at Nakhon Phanom (Thailand), juveniles of about 6 cm were reported to live "near the beach, and when the beach begins to be covered with water, they migrate upstream". They apparently spend the flood season in flooded areas. The same station reported observing juveniles of about 2 cm from March to May.

At Loei, the fish were reported to move up the Loei River and into flooded areas. At that time, juveniles "cannot be seen in the Mekong". From Cambodia, there were several reports of lateral migrations from the Mekong into smaller streams and flooded areas, mainly comprising smaller fish of 20 to 60 cm. At Sambor, juveniles were reported from Lake Sandan, a flood-plain lake.

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