Annual reproductive cycle of mud crab genus Scylla in Marudu Bay, Sabah

Noor Amalia Shaiful Kahar (2016) Annual reproductive cycle of mud crab genus Scylla in Marudu Bay, Sabah. Masters thesis, Universiti Malaysia Sabah.

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Abstract

The knowledge on reproductive biology of wild mud crabs is crucial to understand the reproductive potential in the fisheries and aquaculture industries. The study was conducted to investigate the reproductive biology on sex ratio, maturation stages, breeding season and size at maturity of wild mud crabs Scylla spp. from Marudu Bay, Sabah. Monthly sampling were conducted at Marudu Bay mangrove from October 2012 to September 2013. Mud crabs obtained were transported back to laboratory for further analysis. The crabs were separated into sexes based on the abdominal flap shape and sex ratio was calculated. Morphological and histological observation of the gonad were done to determine the maturation stages and the gonadosomatic index (GSI) and the oocytes size. Size at maturity when 50% of the crabs was sexually mature (SMy-50) were also estimated. A total of 1874 crabs were caught comprises of three species of mud crabs; Scylla tranquebarica, S. paramamosain and S. olivacea. On average, relatively more male crabs caught compared to female crabs; with ratio 2.05:1, 1.17:1 and 2.51:1 for S. tranquebarica, S. paramamosain and S. olivacea respectively. The oocyte size and GSI for S. tranquebarica, S. paramamosian and S. olivacea were almost at similar ranged from 0.64 to 10.70%, 29.19 to 201.33μm. Crabs were classified into immature and mature stages based on gonadal maturation. Five stages in female; stage I and II as immature and stage III to V as mature crabs. While three stages in males; stage I and II as immature and stage III as mature crabs. There also sub-adult crabs found without gonadal development. Based on this maturation classification, all stages of crabs can be found. On monthly basis, it was found that in S. tranquebarica an average of 39.9% and 25.6% for female and male crabs recorded as young crabs. While mature S. tranquebarica crabs were found at average of 28.7 % and 35.0% for female and male. Both female and male S. tranquebarica can be found throughout the year. Percentage of mature female crabs were high in February and May, then followed by sudden decrease in March and June. The same trend was observed in male crabs. This suggest that S. tranquebarica in this area is continuous breeders with possible two breeding seasons. For S. paramamosain, majority of 61.4% and 81.7% female and male caught were young crabs. While only 5.7% and 5.1% was classified as mature female and male crabs. Different from S. tranquebarica, opposite pattern was observed as female crabs were found in certain months and mature male crabs can be found year round. Overall, present study suggest that the sampling area is the suitable area for sub-adult of S. paramamosain to reside while it can also be considered as maturation ground for S. tranquebarica. While for S. olivacea, the reproductive pattern for both female and male crabs was not clearly observed as a consequences of parasite infection that lead to insufficient number of healthy crabs (only 19 crabs for female and 61 crabs for male). Based on all crabs caught, the estimated size at maturity when 50% of the crabs was sexually mature (SMy-50) were estimated at 94.0 mm CW for female and 99.5 mm CW for male S. tranquebarica, 98.9 mm CW for female and 98.4 mm CW for male S. paramamosain and 90.0 mm CW for female and 108.0 mm CW for male S. olivacea. In this present study, based on the estimated SMy-50, 100 mm CW for female and 110 mm CW for male are suggested to be the minimum legal size landing. Information obtained in this study is important in fisheries management of mud crabs in Sabah.

Item Type:	Thesis (Masters)
Keyword:	Mud crab, Scylla, Reproductive biology, Marudu Bay
Subjects:	Q Science > QL Zoology > QL1-991 Zoology > QL360-599.82 Invertebrates
Department:	INSTITUTE > Borneo Marine Research Institute
Depositing User:	DG MASNIAH AHMAD -
Date Deposited:	31 Jul 2024 11:54
Last Modified:	31 Jul 2024 11:54
URI:	https://eprints.ums.edu.my/id/eprint/39305

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