Author: (Durand, 1940)
FBname: Laotian shad
Comments: Inhabits mainstreams, lowland tributaries and floodplains (Ref. 58784).  A riverine species, at least judging from the distance (as far as 2000 km from sea) up the Mekong River.  A filter feeder specializing in microscopic food such as phytoplankton or bacteria found on particulate matter (Ref. 12693) and zooplankton (Ref. 58784).  A ripe male was recorded at Nongkai, Thailand.  Migrate up the Mekong River at Chinese New Year (late January to late February) in company with <i>Cirrhinus</i> spp. and <i>Botia modesta</i> and downstream in June-July with <i>Cirrhinus</i> spp.  Most large spawning fish of 400-500 g weight.  Last recorded large scale migrations was in 1984 and is likely to disappear (Ref. 9497).  Largest individuals are found in the Great Lake and smaller ones in northern Cambodia (Ref. 12693).  In the middle Mekong along the Thai-Lao border, small individuals (young of the year) of 4 to 5 cm TL were first encountered in the middle of April, which by the middle of May had doubled in average size.  By early June, the average  individuals taken in haul seines had a total length of 14 cm, although the consistent recruitment of smaller individuals half that size indicated that spawning period may have extended over more than one month.  The abundance of young of the year increases during the onset of the rising water levels when the suspended solids increase.  This species migrates downstream into Cambodia in July.  It may follow the turbid floodwaters all the way to the Tonlé Sap, perhaps moving into the Great Lake as it fills with water from the Mekong.  As water levels in the Great Lake fall, it migrates back down the Tonlé Sap to the Mekong.  With water flow decreasing, it begins the movement upstream toward Khoné Falls.  Whether or not an individual fish would cover this entire distance is unknown, as is the time required for such journey (Ref. 12693).  Above the Khone Falls, a combination of the first rain, increased water levels and increased turbidity triggers the fish to undertake upstream migration to spawning sites associated with flooded areas in tributaries of the Mekong.  As water starts to recede, it moves back to the mainstream (Ref. 37770).  Its numbers seem to decline drastically for unknown reason, although it may be due to multiple factors including dam construction and over-fishing.  The decline over the two decades may be due to the traps used at Khoné Falls.  However, the previous government in Laos declared the traps illegal in 1968 and destroyed them, allowing fishing only by net and hook-and-line (Ref. 9497).  Fishing improved all along the middle Mekong from Pakse to Vientiane following the destruction of the traps (Ref. 39350).