Background: Yellow catfish, one of Southeast Asia&rsquo;s most economically significant fish, is found in natural water sources in Thailand. Research on genetic diversity is essential for effective aquatic species management. The purpose was to assess the length-weight relationship (LWR) and genetic diversity of yellow catfish (Mystus nemurus) from Nong Han Lake, Thailand.&nbsp; 
 
Methods: 330 samples were collected from ten subpopulations: Ban Tha Rae (n = 31), Don Ang (n = 30), Wat Phon Bok (n = 30), Don Sakhan (n = 32), Don Sao Aey (n = 30), Don Sawan (n = 40), Nguyen Don (n = 32), Lum Nam Phung (n = 40) and Ban Tha Sala (n = 35). Surasawadi floodgate (n = 30). The LWR and feeding intensity were described by the equation W = aTLb and the condition factor (KF) was calculated as KF = 100 W/TLb and RAPD technique was used to evaluate the populations. 
 
Result: The results showed b and KF values ranged from 2.7841-3.6942 and (KF) values from 0.1706-2.0943. 102 DNA bands were identified from RAPD with sizes ranging from 200 to 2,500 bp. Polymorphic loci were found in 71.57% to 98.04%. Nei&rsquo;s gene diversity ranged from 0.24 to 0.36. The genetic distance between reproducible bands of amplified DNA fragments varied from 200 to 2,500 bp. The UPGMA dendrogram of the RAPD-PCR patterns revealed two groups of genetic relationships. The average genetic distance across all samples ranged from 0.020 to 0.245.

Length-weight Relationship and Study using RAPD Technique to Determine the Genetic Variation of Yellow Catfish (Mystus nemurus, Valenciennes 1840) in Nong Han lake, Sakon Nakhon Province, Thailand