AACL Bioflux, 2017, Volume 10, Issue 2. http://www.bioflux.com.ro/aacl 191 The mud crab ( Scylla serrata ) behavior in different inclination angles of funnel and escape vent for trap net Aristi D. P. Fitri, Herry Boesono, Agus Sabdono, Fahresa N. Supadminingsih, Nadia Adlina Faculty of Fisheries and Marine Science, Diponegoro University, Tembalang, Semarang, Indonesia. Corresponding author: A. D. P. Fitri, aristidian@fisika.undip.ac.id Abstract . Mud crab (Scylla serrata) is one of the most valuable commodities among the Portunidae group that is caught by collapsible trap in Semarang, Indonesia. The trap entrance (funnel) is designed to allow adult crabs to pass in and prevent them from passing out, with the help of inclination angles. The other design uses escape vents that allow smaller crabs to escape. The trap used in this experiment was constructed of PE 210D/6 ¾ inch iron rode frame with 20 o , 30 o , 40 o , 45 o and 60 o inclination angles, and 2, 3, 4 cm high escape vents. The objective of this experiment is to analyze mud crab behavior in different inclination angles of funnel and escape vent for trap net. The method used in this research is laboratory experiment of 2 life stages; sub-adult carapace width (CW < 10 cm) and adult carapace width (CW > 11 cm) crabs, by counting the crawling time and escape rate. Results show that the 40 o inclination makes it easier for adult crabs to pass than the sub-adult crab and the 4 cm high escape vent enables 92.30% of sub-adult crabs to escape and keeps 69% of adult crab stuck in the trap. The conclusion found that the slope angle of 40° and a gap for passage of 4 cm providing opportunities mature crabs trapped in trap. Key Words: mud crab, crawling, inclination, escape vent, life stage. Introduction . Mud crab is a member of the Portunidae family (Order Decapoda; Class Crustacea). The growth of crustaceans is characterized by the process of molting. The members of order Decapoda are characterized by the presence of five pairs of legs, the first pair of legs is called claws that act as a catcher/food holder, the fifth pair of legs in a fan shaped (flat) serves as the swimming leg, and the rest are for crawling/walking legs. With the claws and legs, crab can run fast on land and they can swim quickly in water using the swimming legs that they are classified as swimming crab (Mohanty et al 2006). Mud crabs belong to the Scylla genus, which comprise fast growing species that attain larger sizes among portunids and are widely distributed throughout the coastal zones of the Indo-Pacific region (Viswanathan & Raffi 2015). Mud crabs represent a valuable component of traditional, small scale coastal fisheries in several tropical and subtropical Southeast Asian countries which stands as a significant commodity that fetches a high price in the international seafood market (BOBP 1992). Prasad & Neelakantan (1988) explained that carapace width (CW) was used to know the stadia of crabs; < 7 cm for juvenile, 8.1-11 cm for sub-adult and > 11 cm for adult, respectively. Based on the Indonesian Ministry of Fisheries and Marine Regulation No. 1 year 2015 on crab’s legal size, crabs that can be caught must have a carapace width (CW) of ≥ 15 cm or a weight of ≥ 250 gr. The legal size of crabs is determined by the maternity age which can be seen at CW > 11 cm. Therefore, we need to know the inclination on collapsible trap to catch adult crabs. Inclination angle is an important factor that determines how many adult crabs are caught and how many sub-adult crabs can escape. According to Archdale et al (2006a), it is very important to study the crab’s behavior when they entering a trap to understand their responses related to the surrounding conditions. In turn, the escaping habits of the crabs can be understood.