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

Background: The study investigated the Length-weight relationship (LWR), relative condition factor (Kn) and sexual dimorphism in Pristipomoides filamentosus, a deep-water snapper of economic importance in the tropical Indo-Pacific region. 
 
Methods: A total of 891 fish (476 females and 415 males) were collected from the Vizhinjam fish landing centre at the southern tip of Kerala, India and analyzed from October 2022 to March 2023. The cube law and student&rsquo;s t-test were applied to calculate LWR and used to check if there was any significant deviation from the cubic relationship of both female and male P. filamentosus. Month-wise and Length class-wise, mean Kn was calculated to check the health conditions of both female and male P. filamentosus. Body colouration, fin pigmentation and external characteristics of genital papillae and urogenital regions are used to explore the sexual dimorphic characteristics of P. filamentosus. 
 
Result: Growth was negatively allometric and the coefficient of determination (R2) for female, male and pooled sexes were 0.966, 0.976 and 0.970, respectively. The relative condition factor (Kn) was highest for females (1.20&plusmn;0.02) in November and for males (1.17&plusmn;0.02) in October. Additionally, fish with fork lengths (FL) between 49.5-54.5 cm exhibited the highest Kn values for females (1.31&plusmn;0.04), while those with FL ranging from 54.5-59.5 cm showed peak Kn values for males (1.21&plusmn;0.05). The average Kn value for P. filamentosus was approximately one, indicating that the fish were generally in good condition. Sexual dimorphism is more evident in mature P. filamentosus shows characteristic changes in females and males, including body and fin colouration (dichromatism) and external characteristics of the urogenital region and genital papillae. This study provides baseline information and reference points for effectively managing and conserving P. filamentosus.

Exploring the Length-weight Relationship, Relative Condition Factor and Sexual Dimorphism of Crimson Jobfish (Pristipomoides filamentosus) Landed along the Southern Coast of India