Pakistan Journal of Marine Sciences, Vol. 29(2), 99-114, 2020. LIFE-HISTORY TRAITS OF LONG WHISKER CATFISH MYSTUS GULIO (SILURIFORMES: BAGRIDAE) IN THE COASTAL WATER (MALONCHO RIVER) OF SOUTHERN BANGLADESH Obaidur Rahman, Md. Yeamin Hossain, Md. Akhtarul Islam, Md. Ataur Rahman, Dalia Khatun, Most. Farida Parvin, Most. Shakila Sarmin, Sumaya Tanjin, Md. Ashekur Rahman, Zannatul Mawa, Md. Rabiul Hasan, Khatune Zannat, Wasim Sabbir and Md. Abdus Samad Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh (OR, MYH, MAI, DK, MFP, MSS, WS); Department of Fisheries and Marine Bioscience, Faculty of Biological Science and Technology, Jashore University of Science and Techology, Jashore, Bangladesh (ST, MAR, ZM, MRH, KZ, MAS). email: hossainyeamin@gmail.com ABSTRACT: This analysis illustrates the life history traits of Long whisker, Mystus gulio (Hamilton, 1822) including sex ratio, length-weight (LWRs) and length-length relationships (LLRs), condition factors (K A , K F , K R ), relative weight (W R ) and form factor (a 3.0 ), empirical based size at first sexual maturity length (L m ) and natural mortality (M W , year-1). Total of 407 individuals were scarcely collected from January-December 2017 using different fishing gears. The sex ratio (M/F) was calculated as 1:1.26 ( p<0.05). The overall sex ratio did not differ significantly from the expected 1:1(p>0.05). The minimum-maximum total length and body weight were observed as 5.20-15.50 cm and 2.11-33.60g for male, 5.20-17.50 cm and 1.25-57.12g for female. All LWRs were very significant with all coefficients of determination (r 2 )>0.967. The allometric coefficient indicated negative allometric growth in male (b<3.0), positive allometric growth in female and also in combined (b>3.0). All LLRs were significant with r 2 values >0.965. The K F indicated the best condition of this species for their well-being. The W R was not significantly diverse from 100 for males (p = 0.552) and females (p = 0.249), which indicate suitable condition for habitat. The a 3.0 were 0.0103 and 0.0108, and the L m were 9.13 and 10.46 cm in total length for male and female, respectively. Moreover, M W was 1.16 year-1 for male and 1.02 year-1 for female. The results will be operative for the sustainable conservation of M. gulio in Bangladeshi coastal waters and also nearby countries. KEYWORDS: Mystus gulio, population structure, condition factor, size at first sexual maturity, natural mortality, Maloncho River INTRODUCTION The long whiskers catfish, Mystus gulio is a small indigenous species under the Siluriformes order and Bagridae family. This genus is innate to the coastal waters of Bangladesh and the countries of the East Indian Ocean, from India to Indonesia and Vietnam, as well as Pakistan (Talwar and Jhingran, 1991). It is also known as nuna tengra