Int. J. Aquat. Biol. (2016) 4(4): 224-232; DOI: ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2016 Iranian Society of Ichthyology Original Article Allometric growth pattern, sexual dimorphism and size at the onset of sexual maturity in Opusia indica (Brachyura: Ocypodoidea: Camptandriidae) from mangrove areas of Pakistan Noor Us Saher*1, Naureen Aziz Qureshi2, Uroj Aziz3 1Centre of Excellence in Marine Biology, University of Karachi, Karachi, Pakistan. 2Department of Zoology, Government Women College University, Faisalabad, Pakistan. 3A.P.W.A Govt. Degree College for women, Karimabad, Karachi, Pakistan. Article history: Received 7 July 2016 Accepted 8 August 2016 Available online 2 5 August 2016 Keywords: Sexual maturity Somatic growth Intertidal Morphometry Allometry Abstract: Size at sexual maturity and patterns of somatic growth are important aspects of reproductive history of crab. The main purpose of this study is to provide an estimate for the onset of morphological sexual maturity in mangrove crab, Opusia indica from a population located in Korangi creek intertidal mud flat (Karachi, Pakistan) based on relative growth. The crabs were monthly collected through quadrat method from March 2001 to February 2002. A total of 1702 crabs was obtained, of which 764 were males, 939 were female. The morphometric measurement of carapace, abdomen, cheliped and male gonopod was related to carapace width. Based on carapace width males were significantly larger than female, indicating sexual dimorphism. The size at onset of sexual maturity in males was estimated as 5.51 mm carapace width and 5.3 mm carapace width in females. The positive allometric growth of female abdominal width were likely related to the incubation process. Introduction During the course of growth and development in brachyuran crabs, certain dimensions of animal’s body increases at different rates in proportion to size, resulting in a phenomenon known as relative growth. A growth rate between male and female crabs as well as between juvenile and adult crabs shows great differences during ontogeny and can be used to determine morphological sexual maturity (Hartnoll, 1978). The difference in relative growth patterns among male and female crabs for size of chelipeds, abdomen and pleopods indicates sexual dimorphism, and can be used to predict maturity in crab (Hartnoll, 1978; Vannini and Gherardi, 1988; Saher and Qureshi, 2011b). Estimation of size at sexual maturity is key to describe population biology and structure in brachyuran crabs (Pinehiro and Fransozo, 1998). It can be determined by different methodologies i.e. determining morphometric (allometric) changes at * Corresponding author: Noor Us Saher E-mail address: noorusaher@yahoo.com puberty molt (Hartnoll, 1969), gonadal development after attaining maturity (Viau et al., 2006) and functional maturity (Viau et al., 2006). Functional maturity in decapods can be estimated by the determination of ovigerous female in population and situation of actual participation of both in the reproductive process (Viau et al., 2006). Determining the size at sexual maturity in crabs is useful to understand population aspects concerned with abundance, structure and number of mature individuals in a given population as it is responsible by the future generation as well as for researches involves in conservation of biodiversity. Opusia indica (Alcock, 1900) is a small ocypodoid crab of the family Camptandriidae (Ng et al., 2008). These small detritivorous crabs are inhabitant of intertidal mud flat associated with tropical and subtropical mangrove forest (Ng et al., 2009). Crab dig burrows in soft sediment to tolerate harsh environmental conditions as well as refuges 225 Int. J. Aquat. Biol. (2016) 4(4): 224-232 from predators. These burrowing activities help in penetrating air into the deeper sediment layer. Deposit feeding crabs emerge from their burrows when tide descends, there by changing the quality and quantity of resources distributed along the coast in turn play a key role in ecological functioning and environmental management on the intertidal detrital food web (Saher and Qureshi, 2011a, b). The review of literature reveals that there is no previous work on the morphometric studies on these small detritivorous crabs. The aim of the current study is to identify the allometric relationship in male and female crabs of O. indica and also to determine the size at the onset of sexual maturity based on morphological and functional maturity. Materials and Methods Study area: The Pakistan coastal belt is about 1050 km long, with 350 km along Sindh and 700 km along Balochistan coast. Karachi, Pakistan is located on the northern border of Arabian Sea having a coastal belt of about 100 km having Indus delta on its southeastern side and hub river in the west. The coast along the Indus delta consists of numerous dendritic tidal creeks network, including Korangi Creek (24°79'N, 67°20'E) (Fig. 1), located in the South East of Karachi, entouched with a system of creeks in its northeastern side, and open waters on its southern end (Qureshi and Saher, 2012). Mangrove forest mainly comprises of Avicenna marina along creeks coastal zone provides a critical habitat for variety of brachyuran crabs. Field procedures and sampling methodology: Crabs were collected from tidal mud flats regularly from March 2001 to February 2002 through transect quadrat method. During low tide period sampling were done by digging square down to 30 cm. Excavated sediment were sieved (1 mm mesh size), the crab samples were collected in labelled bags and freeze till analyses. Morphometric analyses: For morphometry crabs were initially sorted and sexed (juvenile male (JM), juvenile female (JF), adult male (AM) and adult female (AF), weighed and measured. The carapace dimensions used in morphological analysis were carapace length (CL) (carapace length from anterior median part to posterior carapace margin) and carapace width (CW) (carapace width measured at its widest point). Cheliped dimensions included chela propodus length (Ch.L), Chela propodus width (Ch.W) and Chela propodus height (Ch.H). Abdominal dimensions included abdominal width (width of fifth abdominal somites in male and female crab) and length of first male pleopod (P1) (Fig. 2). All measurements were taken using vernier caliper to the nearest 0.1 mm. Carapace width was used as independent variable which is denoted as X related to other body dimension which were considered as dependent variables Y. The mean values, minimum, maximum and standard deviation were calculated for each variable of female and male and compared by independent (students) T-test. Crab wet weight was estimated using analysis of variance (GLM) to estimate variation among juvenile and adult of O. indica. The relative growth was described using the power function Y=aXb and linearized (log y = log a+b log x) (Huxley, 1950) where “a” is the intercept and “b” is the slope or allometric growth constant. For size weight relationship, exponent ‘b’ represent the weight gain which can be isometric, b=3; positively allometric, b>3; and negatively allometric b<3. The pattern of allometric growth for each developmental phase was established by the ‘b’ Figure 1. Coastal areas of Pakistan showing study site Korangi creek mangrove areas of Pakistan. 226 Saher et al./ Allometric growth pattern and sexual maturity in Opusia indica values, considered as positive allometry when b>1, negative allometry b<1 and growth was considered isometric when 0.9