Inverted migration of rare whisker sheatfish in Nong-Han Lake, northeastern Thailand: implications for conservation

Nong-Han Lake, Thailand, sustains the whisker sheatfish (Micronema bleekeri Günther, 1864), which is a rare species of freshwater catfish. Wild-caught whisker sheatfish has been intensively harvested to meet market demand; yet, genetic information about this species remains unknown. To assist with the in situ conservation of whisker sheatfish populations in Nong-Han Lake, 35 and 34 individuals from the middle (MN) and lower (LN) areas of the lake, respectively, were studied using 7 microsatellite loci. Low genetic variation was detected in the MN (HO=0.338, AR=2.710) and LN (HO=0.394, AR=2.714) populations. Genetic differentiation between the 2 populations was significant (FST=0.063, P<0.05). The size of recent populations (NE<50) was found to be 9- to 29-times smaller compared to the estimated historical populations, even though no bottleneck signal was observed. Low genetic diversity was observed, implying that the populations are at risk of being lost from this site. Of note, migration among the populations inhabiting the middle and lower parts of the lake exhibited opposing trends in changes to the genetic structure. This phenomenon might be due to the operation of a regional irrigation gate over the last decade. The information collected here indicates that the whisker sheatfish populations in Nong-Han Lake require consistent fisheries monitoring and management. Further research about the whisker sheatfish populations from the Mekong and Chao Phraya River basins is required to assist national-scale conservation efforts.