See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/279311890 Current practices in juvenile mud crab rearing Article · July 2013 CITATIONS READS 0 128 1 author: Kok Onn Kwong Universiti Sains Malaysia 15 PUBLICATIONS 7 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Functional Feed Additives and Their Mode of Actions in Mitigating Acute Hepatopancreas Necrosis Disease in White Shrimp, Litopenaeus vannamei View project The Use of Probiotics to Optimize Mud Crab Scylla paramamosain Larval Culture. View project All content following this page was uploaded by Kok Onn Kwong on 30 June 2015. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. JULY/AUGUST2013 Volume 9 Number 4 Acute Hepatopancreatic Necrosis in Shrimp explained Indonesia Lifts Shrimp Production Ocean raised Seabass branded with Singapore Economical Value of Raw Materials in Tilapia Feeds A Changing White Fish Market in Europe MICA (P) 008/10/2012 PPS1699/08/2013(022974) www.aquaasiapac.com By Kwong Kok Onn In Malaysia, the growing interest in farming of the mud crab is hampered by supply of hatchery reared juveniles. A juvenile mud crab after several moults following the C1 stage, ready to be stocked into growout culture. Picture courtesy of Muhamad Syahmin Aiman. The genus Scylla includes the species Scylla serrata, S. tranquebarica, S. olivacea and S. paramamosain. The four species can be differentiated through their external morphology. Scylla serrata, S. tranquebarica and S. olivacea are common in the Philippines whereas S. paramamosain is common in Vietnam, Indonesia and Thailand. All species are suitable for aquaculture and are farmed commercially. In Malaysia, the most common species are S. olivacea, S. tranquebarica, and S. paramamosain. Mud crabs have shown great possibility as a commercial aquatic product in many Southeast Asian countries. However, the farming is mostly carried out on a small scale by local fishermen, and is mainly based on the rearing of wild captured crablets to marketable sizes. This crustacean is regarded to be among the best eating of crab species, and predictably, wild stocks of Scylla in many countries are overfished and overexploited. World aquaculture production of crabs increased from 44,766 tonnes in 1995, to 254,395 tonnes in 2010, with a value of USD 228,636 and USD 808,448 respectively (FAO, 2012). Currently, mud crab aquaculture is an upcoming industry in Malaysia. The average price for mud crabs selling at a typical farm in Malaysia is currently MYR 13–16/kg (USD 4.1-5.1/kg) for 200-290 g crabs, MYR 20-23/kg for 300-390 g, and MYR 31-51/kg for 400-500 g. Average wholesale price in 2010 was MYR16.73/kg, and retail price was MYR 19.86/kg (Department of Fisheries, Malaysia). A berried mud crab can cost MYR 30-40 each (USD 9.7-12.9). Currently, the insufficient supply of mud crab juveniles from wild stocks is one of the main reasons for the decline in mud crab aquaculture in Malaysia. Production declined from 600 tonnes in 1999 to 29.53 tonnes in 2010 (Fishstat Plus and DOF, Malaysia). In order to promote its aquaculture, hatchery raised juveniles are required. into the megalopa and the first juvenile or crablet stage (crablet 1 or C1) through another two moults. It takes 23-24 days at 26-29 ºC for the zoea to develop into the C1 stage, 4-5 days from zoea 1 to zoea 5, and 6-7 days from megalopa into the C1 stage. The zoea stage is the planktonic phase and megalopa stage is the start of the benthic phase. The mud crab then undergoes a series of moults to reach the adult stage. This takes around 3 to 4 months to attain the market size of above 250 g. The nursery stages of Scylla include one megalopa (M) stage and several crab instar (C) stages. This article will mainly cover nursery culture from the M to C1 stages, as this is considered the critical period, where mortality during molting can be high (mud crabs are fairly hardy once they reach the C1 stage and beyond). Previous survival rates from M to C1 obtained at the Centre for Marine and Coastal Studies (CEMACS), Universiti Sains Malaysia (USM) ranged from 5.0-58.0%. Nursery practices In the Phillipines, megalopae are cultured in concrete tanks or in net cages set in brackish water ponds. Ponds are prepared for culture using the original protocol of Trino and Sarroza (1995), as follows: the pond bottom is sun dried for 5 to 7 days or until the soil cracks. After application of agricultural lime and chicken manure at 1 tonne/ ha each, the pond is filled with water to around 30 cm depth. When a good bloom of phytoplankton is obtained, water volume is increased to 80 cm deep over a 3- day period. In order to sustain plankton growth, pond water is fertilised with the same dose of fertilisers every 10 days. Ponds are advantageous because they provide wider surface areas for the scattering of the megalopae, assuming that the ponds are predator free and have enough natural food. Net cages (mesh size 1 mm, bottom surface area 20 m2) are set in the ponds for the megalopae. Bamboo poles are used to hold up the cages and the net bottom is buried 3-5 cm into the pond soil. A good bloom of phytoplankton and zooplankton is achieved around 7 days following the use of organic fertiliser at 1 tonne/ha and inorganic fertilisers, urea (45 - 0 - 0) at 75 kg/ha and ammonium phosphate (16-20-0) at a ratio of 1: 2 (urea to ammonium phosphate) or 75 kg to 150 kg/ha, respectively. Life cycle The mud crab begins its life as a zoea after hatching from an egg, and this phase has five stages, termed zoea 1 to 5. Zoea 5 then transforms Figure 1. (A) Scylla paramamosain at the megalopa stage. (B) The first crablet stage of Scylla sp. Pictures were taken from CEMACS. July/August 2013 AQUA Culture Asia Pacific Magazine | 45 DEVELoPMENTS Current practices in juvenile mud crab rearing DEVELoPMENTS Megalopa to crablet Three to five day-old megalopae (around 4.0-6.4 mg initial body weight) are transported in plastic bags at 200-300 ind/L stocking density. Megalopae are transferred to the pond area, and are slowly acclimated to the pond water salinity (24-30 ppt) and temperature (25-30 °C). The targeted pH in the pond is around 7.5-8.5. Megalopae are then stocked in units of 20 m2 (4 m×5 m) net cages installed in a 1,000 m2 brackish water nursery pond. The net cages have 1 mm mesh size and the inner side of the upper end of each net fitted with 30 cm wide plastic sheet (gauge 14) to prevent juveniles from escaping. Bamboo poles are used as support to these cages. Six dried coconut fronds are positioned in the water column in each cage serving as hides for the megalopa or C1 stage. Megalopae are stocked at a density of 30/m2, and water depths are maintained at 60-80 cm. About 30% of the water is changed every week. In addition to ponds, nursery culture can also be done in tanks. Cement composite tanks, and earthen flat-bottomed tanks with plastic lining, with surface areas of 1-10 m3 have been used successfully in Vietnam. To reduce cannibalism, the stocking density of 3-5 day-old megalopae in nursery tanks is reduced to 1,000- 2,000/tonnes of water (10-20 ind/m2). Black, nylon and bunched netting are placed at the bottom as shelter, and some are allowed to float in the water column. (A) (B) Acknowledgements (C) Figure 2. (A) One tonne tanks for mud crab nursery culture. (B) Substrates inside tanks for juveniles. (C) Culturing mud crab megalopa to the crablet stage in tanks, with megalopa visible on the tank bottom. Pictures were taken from CEMACS. Feeds and feeding A summary table of various feed types used by various culturists to culture M to C1 stages is presented in Table 1. From the C1 stage onwards, Scylla are fed minced trash fish, mussel, or small shrimp Acetes sp. two times a day to satiation. Feed rations are equally divided and given at 0800, 1300 and 1700 h daily. Furthermore, zooplankton species can be sampled inside and outside the net cages. The plankton samples are preserved in 5% buffered formaldehyde for examination under a microscope, and the dominant species noted. The survival rates from megalopa to several instar stages are 35–50% in hapa nets within earthen ponds, and 50% in pens. Table 1. The regime used during the megalopa stage as adopted by various culturists in the nursery culture of Scylla. Crab species S. serrata Scylla sp. Initial stocking density (nos/L) 20 – 30 100 - 300 Feeding rate Survival (%) (nos/mL or % M – C1 BW/ day) 25 A + AF5 5 – 10 A + AF6 S. serrata 30 - 50 5A 32.8 ± 4.8 Scylla sp. 50 0.5 - 3 A 30.0 – 50.0 S. serrata 10 – 30 30 MM1 48.3 - 53.3 46 | July/August 2013 AQUA Culture Asia Pacific Magazine The author would like to gratefully acknowledge his supervisors Dr Anita Talib and Dr Md. Arif Chowdury, and express his kind appreciation to the other team members of CEMACS involved in the mud crab project. References Ngoc-Hai T (2011) Seed production of mud crab researches and practices in the Mekong Delta, Vietnam (presentation). College of Aquaculture and Fisheries, Can Tho University, Vietnam. Quinitio ET, Parado-Estepa FD, Millamena OM, Rodriguez E, & Borlongan E (2001) Seed production of mud crab Scylla serrata juveniles. Asian Fisheries Science 14: 161-174. Quinitio ET, Parado-Estepa FD, Rodriguez E (2002, July-September) Seed production of mud crab Scylla spp. Aquaculture Asia 7(3): 29-31. Rodríguez EM, Quinitio FD, Parado-Estepa FD, Millamena OM (2001) Culture of Scylla serrata megalops in brackishwater ponds. Asian Fisheries Science 14(2): 185-189. Other references available on request. Author Jamari (1991) Ngoc-Hai (2011) Quinitio et al. (2001) Quinitio et al. (2002) Rodriguez et al. (2001) A: Artemia sp. AF5: SUTIMAL, feed for giant freshwater prawn (protein 55 %, fat 8 %, ash 7 % and moisture 5.5 %), at 7 - 12 g/ ml. AF6: Frippak, Lansy, 150 – 500 µm, 1 – 5 g/ m3 daily. MM1: marine meat macerated brown mussel meat (Modiolus metcalfei) or fish. View publication stats During the culture period, pond water depth is held at 60-80 cm. About 30-50% of the pond water (26-30 ppt.) is replaced daily during the first 5 days, and every 2 days thereafter, taking opportunity of spring tides. Using many hatchery tanks for nursery culture at low densities is not cost effective, because these tanks are better utilised for larval culture, which can have a shorter culture period. Pond water salinity, temperature, pH and dissolved oxygen are monitored three times weekly at 0900 h, with targeted salinities of between 24-30 ppt. Weight sampling of crablets is done by lifting the net cages after 20 days of culture. After 30 days, crablets are harvested by discarding 70% of the pond water and lifting each net cage. Survival and mean individual body weight of the crablets is determined in each cage. Mass weight is also determined from the total weights of crablet in each cage. The survival from M to C1 (1-3 g body weight (BW)) after 30 days in hatchery tanks or pond cages is around 30-50%. A large number of C for grow out can be obtained if megalopae are cultured in net cages within ponds. The duration of nursery culture from M to C1 stage can take up to 9 days. The survival rates is during the nursery culture phase, which is usually from the megalopa to several crab instar stages. Currently, one of the major constraints worldwide to the expansion of the mud crab culture industry is the bottle neck in juvenile supplies from hatcheries. Although some research groups have some success in the mass production of mud crab juveniles, consistent and reliable commercial culture has not yet been achieved so far. Therefore, further research and development are required before commercial mud crab hatchery culture becomes economically viable and widely adopted. Kwong Kok Onn is a research assistant and Masters student at the Universiti Sains Malaysia (USM)’s Centre for Marine and Coastal Studies (CEMACS) in Muka Head, Penang, His project involves the use of probiotics to optimise mud crab Scylla sp. larval culture. He has a B. Aquaculture (Hons) from the University of Tasmania, Australia. Email: kokonn.kwong@gmail.com