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Gonad Development and Size at Maturity of the Male Mud Crab Scylla Paramamosain (forsskål, 1755) in a Tropical Mangrove Swamp

Md. Sherazul Islam
Department of Fisheries and Marine Bioscience, Faculty of Biological Science and Technology, Jessore University ofScience and Technology, Jessore-7408, Bangladesh

Hisashi Kurokura
Laboratory of Global Fisheries Science, Department of Global Agricultural Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan2 Laboratory of Global Fisheries Science, Department of Global Agricultural Sciences, Graduate School of Agriculture andLife Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan

Abstract/ Executive Summary:

The reproductive traits and size at sexual maturity of the male mud crab Scylla paramamosain were investigated in Pak Phanang mangrove swamps, Thailand. Samples were taken seven times from the local middlemen mud crab traders during June 2006 to January 2008. Gonad development was determined based on histological appearance that was classified into three stages: 1) Immature (Spermatogonia), 2) Maturing (Spermatocytes) and 3) Mature (Spermatids and Spermatozoa). Among the sample population, the highest 72% was under gonad development stage I, whereas mature stage III was only 12%. The size at first maturity was estimated by the external allometric growth and histological observation of gonad. The size at which 50% of individuals attain sexual maturity was estimated by the two mathematical models such as probit analysis and logistic curve. The mean size at first sexual maturity and 50% maturation of male S. paramamosain were 96 mm and 109 mm internal carapace width (ICW) which revealed that 88% individuals were immature. The present result suggested that the minimum legal size of male S. paramamosain capture should be >110 mm ICW.

Keywords: Reproductive traits, Scylla paramamosain, Legal capture size, Mangroves

Location:

Start Date: 00-06-2008

End Date: 00-01-2010

Program Area: Animal Health and Management

Commodity: Carp fish

Objectives:

To conduct the present study to provide detailed reproductive information of male mud crab.

Methodology:

Sampling: Male S. paramamosain were collected during June 2006 to January 2008 from the local mud crab middle trades of Pak Phanang estuary, Nakhon Si Thamarat, Southern Thailand. Crab fishing is conducted throughout the year within mangrove channels as well as associated channels connected to the bay. In the present study, survey was focused on the communities within the mangrove. In the laboratory, 81 male crabs were examined which did not include any morphological anomalies. The following measurements of body size were taken with a digital caliper to the nearest 0.1 mm: internal carapace width (ICW), lower paddle width (LPW), propodus length (PL) and chela height (CH) of left cheliped. Histological study: Tissue from the middle vas deferens/testes from each male was dissected and preserved in Davidson’s fixation for further histological examination. The tissues were dehydrated in ascending ethanol concentrations from 70 to 100%, transferred to Lemosol (Wako Pure Chemical Industries, Osaka, Japan) and embedded in paraffin. The tissues were sectioned to 5 μm and stained with Mayer’s hematoxylin–eosin (HE). The histological stage of development was determined by making reference to those of other crustaceans (for example, Lestang et al. 2003, Mura et al. 2005; Viau et al. 2006 and Islam and Kurokura 2012). The development stages of the gonad were determined by the macroscopic appearance based on the formation of spermatocytes and presence of spermatozoa. Estimation of size at maturity: The middle vas deferentia were used for the histological study and maturity estimation. Sexual maturity was classified with the visibility of vas deferentia and the presence of spermatophores within their lumina. The relative frequencies of each stage of sexual maturity in the samples were analyzed to describe the reproductive cycle of males. The size at first maturity was estimated by three methods that are described following: 1. Allometric increments proportional to ICW; the allometric growth increments of CH, PL and LPW were plotted against the increments of ICW and existence of the flexion point was investigated and treated at the size of first maturation in male crab. 2. The minimum size at maturity recorded through histological studies of the male mud crabs (> 70 mm ICW). 3. Chela height (CH)/internal carapace width (ICW) index is another method which calculated as the divides of CH by ICW. The samples were categorized to two groups by the critical point of CH/ICW and the histological developments of the gonad were compared between two groups. Regression analysis was performed to determine the relation of Chela height (CH) with internal carapace width (ICW). A significant level of P> 0.05 was considered.

Source of Information: Journal of Fisheries, Volume 1 Issue 1 Pages: 7-13 December 2013

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The size at first maturity was estimated by the external allometric growth and histological observation of gonad. The size at which 50% of individuals attain sexual maturity was estimated by the two mathematical models such as probit analysis and logistic curve. The mean size at first sexual maturity and 50% maturation of male S. paramamosain were 96 mm and 109 mm internal carapace width (ICW) which revealed that 88% individuals were immature. The present result suggested that the minimum legal size of male S. paramamosain capture should be >110 mm ICW.

Knowledge Management: Journal