~ 451 ~ International Journal of Fisheries and Aquatic Studies 2018; 6(4): 451-455 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2018; 6(4): 451-455 © 2018 IJFAS www.fisheriesjournal.com Received: 23-05-2018 Accepted: 24-06-2018 Sheik Istiak Md. Shahriar Department of Aquaculture, Hajee Mohammad Danesh Science & Technology University, Bangladesh Muhammad Abdur Rouf Fisheries and Marine Resource Technology Discipline, Khulna University, Bangladesh Correspondence Sheik Istiak Md. Shahriar Department of Aquaculture, Hajee Mohammad Danesh Science & Technology University, Bangladesh Sex ratio, length-weight relationship, condition and relative condition factor of mud crab (Scylla olivacea) in Sunderban mangrove forest, Bangladesh Sheik Istiak Md. Shahriar and Muhammad Abdur Rouf Abstract This study was attempted to determine the basic biological information on Scylla olivacea collected from Sunderban mangrove forest, Bangladesh during a period of May-October 2016. The average length of male and female crabs was 87.48 mm and 79.86 mm with an average weight of 173.15 g and 97.15 g, respectively. Although the sex ratio of this species remained uneven throughout the study, highest (male: female=1:3) was recorded in 70-79 mm size range. In length-weight relationship, the coefficient determinant (r 2 ) for male was 96.5%, for female was 98.2%, and for combined sexes was 93.9%. The value of exponential ‘b’ at 95% confidence interval was 3.222-3.45 in male, 2.618-2.748 in female and 3.06-3.261 in combined sexes. A strong positive correlation was observed in length-weight relationship of three different sexes. The value b observed in combined sexes resulted that the growth of these organisms was close to isometrics. The average condition factor (K) in male was 0.025 and in female was 0.019 and but the Kn of male was 0.0000057 and female was 0.00014. The obtained K value suggested, males were much heavier than female at the same length. However, this study will be helpful to understand the biological status of Scylla olivacea fishery in Sunderban mangrove forest, Bangladesh which ultimately could be used in the management of mud crab resources in this forest. Keywords: Length-weight relationship, condition factor, Scylla olivacea, Sunderban, Bangladesh 1. Introduction The mud crab, genus Scylla is extensively distributed in the muddy river, tributaries, canals and intertidal areas of mangrove wetlands in Indo-Pacific regions [13, 17] . In Bangladesh, after a long controversy on taxonomic classification on genus Scylla; recently, it has been confirmed that S. olivacea is the common mud crab species being caught from Sunderban mangrove forest [21] which was mistakenly addressed as S. serrata in earlier literature by many researchers [20] . Since, the taxonomic clarification of this species is stated; exploration for significant biological features of this species is now paramount in importance. Length-weight relationship and condition factor provide useful information to understand the dynamics of a fishery in a given ecosystem. Moreover, data on length-weight relationship has significance in determining the actual dimension of a crustacean stock [3, 11] and it also helps to determine the growth performance; more explicitly present condition, maturity, feeding rate, spawning frequency, their suitability to environment and so on [6, 8, 22] . Condition factor is more suitable in comparing the physical condition of an organism to that of others. In addition, it refers to the assumption that the higher weight at the same length provides much better condition in terms of growth [19] . In recent years, capture of wild mud crab has been expanding because of its high export value in international market. Consequently, the wild population is being subjected to enhanced exploitation for last few decades to meet the increasing demand [2] . Due to its high economic value, several Bangladeshi researchers conducted studies dealing with morphology, general biology, taxonomy, molecular systematics, distribution, biochemical analysis, catch per unit effort, culture and marketing [1, 7, 10, 12, 20, 21] . However, the extensive information on population features of this species is lacking. This present investigation, therefore, aims to provide useful biological information regarding sex ratio, length-weight relationship, condition factor and relative condition factor of Scylla olivacea found in the Sunderban mangrove forest, Bangladesh.