AACL Bioflux, 2014, Volume 7, Issue 3. http://www.bioflux.com.ro/aacl 148 AACL BI OFLUX Aquaculture, Aquarium, Conservation & Legislation International Journal of the Bioflux Society Length-weight and width-weight relationship of spiny rock crab Thalamita crenata (Crustacea, Decapoda, Portunidae) in Panjang Island Banten Indonesia Adi Susanto, Ririn Irnawati Department of Fisheries, Agriculture Faculty, Sultan Ageng Tirtayasa University, Serang Banten Indonesia 42122. Corresponding author: A. Susanto, adisusanto@untirta.ac.id Abstract . This research performed to determine length-weight and width-weight relationship of spiny rock crab ( Thalamita crenata) caught at Panjang Island. The total number (1,368 crabs) used as sample consists of 838 males and 530 females. Carapace length has significant correlation with weight, where r² for males and females are 82.36% and 71.50% respectively. The correlation of length-weight and width- weight relationship at males is higher than females because many crabs still at maturity stage. The ovarian stage will affect to total mass tremendously. T-student analysis that shows growth pattern for males is isometric and negative allometric for females, with b value of males 3.0278 and females 2.729. It also means the male crabs are heavier than the females. Key Words: carapace, correlation, growth pattern, isometric, negative allometric. Introduction . Thalamita crenata (Latreille, 1829) or spiny rock crab is the common crab that inhabits the mangrove and shallow water of the Indo-Pacific to coastal of Africa (Chande & Mgaya 2003). It is often caught as by-catch at trap and gillnet of mangrove carbs ( Scylla sp.) and swimming crab ( Portunus pelagicus) in Panjang Island. It is smaller than mud crab and has lower economic value. Nevertheless, this crab is one of the main commodities in traditional market in Thailand and Africa (Songrak et al 2010). Length-weight and width-weight relationships are an important aspect in fisheries biological investigation, ecology, and suitability of its environment (Mohapatra et al 2010; Thirunavukkarasu & Shanmugam 2011). In addition, morphometric and weight relationship can also be used for investigating growth model. Food and feeding habits can also be identified from length and weight cluster differences (Thirunavukkarasu & Shanmugam 2011). There have been many investigations in length-weight and width- weight of mangrove crabs or swimming crabs (Thirunavukkarasu & Shanmugam 2011; Pinheiro & Hattori 2006; Josileen 2011; Ribeiro et al 2013). Regarding to other research, natural diet and feeding habit of T. crenata was conducted by Cannicci et al (1996) and biochemical changes in larval stage of T. crenata by Kannupandi et al (2000). This study aims to analyze relationship of length-weight and width-weight of T. crenata from Panjang Island Banten Indonesia. Material and Method . The experimental fishing was conducted from January to February 2014 in mangrove water of Panjang Island. The collapsible trap was used to collect samples of spiny rock crabs. The 15 days fishing trials got 838 males and 530 females whose carapace length/CL (mm), carapace width/CW (mm), and weight/W (g) were measured. Length-weight and width-weight relationship were separately for males and females by the least square method using natural logarithmic transformation (ln). The exponential equation for length-weight relationship is ; width-weight relationship ; “a” is constant (intercept) and “b” is coefficient of length/width