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Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 12 (2018) Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2018.712.100 Morphometrics and Length-weight Relationship of Charybdis natator from Gulf of Mannar, India V. Vidhya1, P.Jawahar1* and K. Karuppasamy2 1 Department of Fisheries Biology and Resources Management, Fisheries College and Research Institute, Thoothukudi 628008, India 2 ICAR-CMFRI, Tuticorin Research Centre, Tuticorin -628 001, India *Corresponding author ABSTRACT Keywords Charybdisnatator, Morphometric, Characters, Relationship, Positive correlation, Gulf of Mannar Article Info Accepted: 07 November 2018 Available Online: 10 December 2018 The length - weight relationship of Charybdis natator (Herbst, 1794) was studied from Gulf of Mannar for a period of one year. The interrelationship between carapace width, carapace length, chelarpropodus length, weight and abdominal width in males as well as females, were estimated. Fishing activities are carried out throughout the year. The carapace width of the crabs ranged from 2.4 cm to 12.8 cm, carapace length ranged from 1.9 cm to 9.5 cm and the weight ranged from 20 to 659 g. The smaller sized male and female C.natator species were recorded during October and February respectively. The coefficient of correlation (r) obtained for the carapace length-weight (Male - 0.910; Female - 0.837; Pooled data- 0.902) and carapace width -weight of males, females and pooled data were nearly equal to 1 (0.928, 0.913 and 0.934 respectively) indicating that the values were significant and hence, high degree of positive correlation existed between width weight and length-weight in these crabs. Analysis of covariance of carapace width - weight data in the species between the regression equations in males and females were highly significant. The present results indicated that males are heavier than females at any given length / width in this species. Introduction Crustaceans are a diverse group of arthropods and many crustaceans are of great direct and indirect important to humans because of their large role in marine food chains. Crabs are one of the commercially important crustacean groups. A total of 990 species of marine brachyuran crabs belonging to 281 genera and 36 families were reported from Indian waters (Kathirvel, 2008). In India, the fishery of edible crabs is sustained mainly by crabs of the family Portunidae. They are caught as a bycatch in trawling as well as main catch by the specialized bottom set gill nets, locally known as ‘nanduvalai’ in the Gulf of Mannar. There are 238 brachyuran crab species so far recorded in the coral reef areas of Gulf of Mannar. In Gulf of Mannar region C.natator was recorded throughout the year with peak during the month of in October and May for male and September for females. C.natator 797 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 occurs from the intertidal zone (especially juveniles) to depths of 15-35 m. It inhabits sandy / pebbles/rocky bottom, and also in brackish water subtropical and tropical climates. The portunid crab C. natator exists in the commercial catches of the Gulf of Mannar. Although edible worldwide, this crab is hardly known among local consumers. The interrelationships between various morphometric characters, viz., carapace width/length and chelar propodus length in males and carapace width/length and abdominal width/length in females were analyzed and presented. The results will be useful in comparing the different stocks of the same species at different geographical locations. Hence, it will be pertinent to describe the fishery of this important resource and also to study the growth and stock characters of the portunid crabs off Gulf of Mannar coast. Materials and Methods Study area The present study was carried out for a period of 12 months from June 2015 to June 2016 from part of the Marine biosphere of Gulf of Mannar (8° 35' N - 9° 25' N latitude and 78°08' E - 79° 30' E longitude), South East coast of India. Sample collection Charybdis natator samples were collected from four landing centers at Gulf of Mannar coast. The sample stations are Therespuram, Vellapatti, Vedalai and Periyapattinam. Fortnightly samples were taken from these landing centers (Fig. 1). The crabs were collected up to 10 to 15 nm from the sea shore in Gulf of Mannar region. From these stations sample of C. natator (Fig. 2) were collected and each crab was measured and recorded for its sex, carapace width, carapace length, abdomen width, chelate length and body weight by using Vernier calipers with an accuracy of 0.5 mm. Carapace width (CW) was taken as the distance between the tips of the posterior most lateral carapace spines. Carapace length (CL) was measured dorsally along the midline, between the frontal notch and the posterior margin of the carapace. Right chelar propodus length (Ch L) was measured from the tip of the propodus fixed finger to the base of the propodus. The craft employed along the Gulf of Mannar coast includes trawlers, vallam, and small boats (vathai). Main gears employed in the crab fishery are crab traps, bottom set gill net, and trawl nets etc. A total of 786 C. natator were collected for this study and of these 547male and 239 female of C. natator. A scatter diagram each for males and females in respect of C.natator was obtained by plotting the weight against width and weight against length of individual crabs. From the closeness of the scatter and from the parabolic nature of plot, it is inferred that there exist a good relationship between width and weight, and between length and weight, as also the suitability of fitting the exponential formula, W=a Lb to the data. The data of all specimens were pooled and the relationships between the different set of variables was calculated on the basis of individual measurements. The ‘t’ test was used to find out the significant differences if any, between Carapace width- weight relationship of male and female. Results and Discussion Size composition Totally 786 individuals of C. natator were collected for the present study of which males constituted 69.59% (n=547) and females 30.4% (n=239) respectively. The stock is composed of larger sized males compared to females and dominated by small female individuals in number. The carapace width ranged from 2.4 cm to 12.8 cm, carapace 798 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 length ranged from 1.9 cm to 9.5 cm and the weight ranged from 20 to 659 g. The smaller sized male and female C.natator species were recorded during October and February (Fig. 5, 6 and 7). The size range of the crab C. natator in the gill net fishery of the Gulf of Mannar varying between 2.4 to 12.8 cm Carapace width (CW) for males and from 5.1 to 11.8 cm for female, the carapace length ranged from 2.3 cm to 9.5 cm for male and for female it ranged from 1.9cm to 8.6 cm and the weight ranged from 20 to 659g for male and 28-268 for female was recorded during the present study. 0.902) and carapace width -weight of males, females and pooled data were nearly equal to 1 (0.928, 0.913 and 0.934 respectively) indicating that the values were significant and hence, high degree of positive correlation existed between width- weight and lengthweight in these crabs. The ‘b’ values of male (3.387) and female (2.958) of C.natator were analyzed against ‘3’ with 100 degrees of freedom and which indicates that the ‘b’ value were highly significant at 1% and 5% level (Table 1). Carapace length – Carapace width (CW) relationship Length / width – weight relationship The scatter diagram for males and females was obtained by plotting weight against carapace width/length of individual crabs. From the data, a distinct relationship was found between width and total weight. The morphometric relationship was estimated for carapace length, width, chelate length–weight relationships and carapace length-width, carapace length-chelate length, carapace length, width – abdomen width relationships for male, female and pooled data of C. natator (Fig. 3 and 4). Carapace length/ width – body weight relationship The carapace length (CL) of C. natator was plotted against the weight (Wt) to estimate the CL-Wt relationship. CL varied from 2.3 cm to 9.9 cm for males and from 1.9 to 8.6 cm for females in C. natator while the Wt varied from 20 to 659 g for males and from 28 to 268 g for females. The carapace width of C. natator was plotted against the weight to estimate the CW-Wt relationship. In C. natator the (carapace width) CW varied from 2.4 to 12.8 cm for males and from 5.1 to 11.8 cm for females. The coefficient of correlation (r) obtained for the carapace length -weight (Male - 0.910; Female - 0.837; Pooled data- The carapace length and width had a linear relationship with the following equations. Male :CW = 0.030 +1.449 CL(R² = 0.925) Female :CW = 0.078 + 1.437CL(R² = 0.936) Pooled data :CW = -0.005+1.454CL (R² = 0.934) Carapace length relationship – Chelate length The relationship with carapace length (CL) and chelate length were estimated as below. The R2 values of male, female and combined of C. natator were 0.617, 0.708 and 0.614 for respectively. Male :CL =-2.464 +1.556 CL (R² = 0.617) Female :CL =-0.771+1.145 CL (R² = 0.708) Pooled data: CL =-2.643 +1.557 CL (R² = 0.614) Carapace length – Abdomen width (AW) relationship The allometric growth equations relating to carapce length – abdomen width relationship for male, female and pooled data of C. natator were given below. The R2 values of male, female and combined of C. natator were 799 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Carapace width – abdomen width relationship for male, female and combined of C. natator were presented in Figure 3. The R2 values of male, female and pooled data of C. natator were 0.398, 0.141 and 0.161 respectively. 0.42, 0.167 and 0.178 for respectively indicating a weak positive correlation. Male: AW = 1.304 + 0.294CL (R² = 0.420) Female: AW = 1.800 + 0.301CL (R² = 0.167) Male: AW = 1.446 + 0.187 CW (R² = 0.398) Pooled data: AW = 1.997 +0.206CL (R² = 0.178) Carapace width relationship – abdomen Female: AW = 1.917 + 0.195CW (R² = 0.141) width Pooled data: AW = 2.132 +0.127CW (R² = 0.161). The allometric growth equations relating to Table.1 Carapace width /length –total weight relationship in males and females of Charybdis natator Carapace width –Total weight Male W = Allometric (+) 3.387 0.104L Female Combined Carapace length –Total weight W = 0.346L3.428 Allometric (-) Chelate length - Total weight W = 6.437L1.703 Allometric (-) Carapace width –Total weight W = 0.245L2.958 Isometric Carapace length –Total weight W = 0.758L2.939 Isometric Chelate length - Total weight W = 11.88L1.306 Allometric (-) Carapace width –Total weight W = 0.110L3.356 Allometric (+) Carapace length –Total weight W = 0.365L3.388 Allometric (+) Chelate length - Total weight W = 6.221L1.713 Allometric (-) Table.2 Length-weight relationship of Charybdis natator (Test of significance) Sex Standard Error (S.E) Slope (b)-3 t = (b-3/S.E) Male 0.5187 0.387 0.1317 Female 0.3274 0.042 0.1282 800 Table ‘t’ value 1% 5% 2.626 1.660 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.1 Sampling stations at Gulf of Mannar (not to scale) Fig.2 Charybdis natator 801 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.3 Morphomertric relationship of Charybdis natator 802 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.4 Morphomertric relationship of Charybdis natator 803 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.5 Monthly size (Carapace length) frequency distribution for male and female C. natator in the study area 804 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.6 Monthly size frequency (Carapace width) distribution for male and female C. natatorin the study area 805 Int.J.Curr.Microbiol.App.Sci (2018) 7(12): 797-808 Fig.7 Monthly weight (Wt) frequency distribution for male and female C. natator in the study area 806