LIRONG’S CRAB PAGE

 

Hi. My name is Lirong Yu Abit. I am a biologist specializing in crustaceans.I graduated form Universiti Sains Malaysia in 2001 with an Honours Degree in Applied Science (Aquatic Biology). I am currently pursuing my Masters in Universiti Putra Malaysia, Serdang while working as a Demonstrator. I used to work as a research officer for the Department of Agriculture Sarawak (Inland Fisheries Branch) in Sematan working on two projects. An Industrial Grant Scheme (IGS) project on the Seed Production of Mud Crab (Scylla spp.) and an Industrial Research into Priority Areas (IRPA) project on the Seed Production of Blue swimming crab (Portunus pleagicus). I created this page to post the results of some experiments that I carried out during my time as a research officer. The format of writing is mainly as lab reports.

 

Email:

[email protected]

 

 

                                                            That’s Me Capturing A Berried Female Mud Crab

 

Here is an initial study of the Crucifix Crab (Charybdis feriatus)

A picture of the crucifix crab

Larviculture of the Crucifix Crab Charybdis feriatus in laboratory

Lirong Yu Abit and Che Roos Saad

Introduction.
Charybdis feriatus is the most commercial species in the genus Charybdis. It is widely distributed throughout the Indo West Pacific region reaching until Japan and Australia. In East Asia the crab fetches a price from US$8 to US$15 per kilogram (Ng, 1999). Currently this species has not been cultured commercially but has good potential for aquaculture due to its large size, taste and meat quality. Charybdis feriatus can easily be distinguished by its striking red and black color pattern. This crab is often captured at depths of 30-60 meters by fishermen using gillnets or bottom trawls. Studies towards the production of this species have been carried out at SEAFDEC/AQD Hatchery in the Philippines  from July 2000 and reported a survival rate of 2% - 5% from Zoea 1 to Crab 1 stage. (Estepa et al., 2002). This study was carried out in The Department of Agriculture (Inland Fisheries Unit), Sematan from August 2003 till September 2003 to asses the viability of this species for mass culture.

Materials and Methods

Berried female crabs (150 to 250 grams bodyweight) with large orange egg mass were captured from the wild and disinfected with 100 ppm of formalin for 30 minutes before being transferred into 0.5 ton spawning tanks located within a darkroom. Daily water exchange of 100% was carried out until hatching, during this period crabs were not fed. After 7-10 days hatching occurred. Healthy (strong swimming) larvae were transferred to 10 liter flat bottomed plastic basins at a stocking density of 100 pieces/liter, the study was carried out in triplicate. Larvae were fed once daily using the feeding regime described in Table 1. Feeding was carried out ad libitum once daily.

Table 1: Larvae rearing feeding regime*1
Larval Stage Feed Artificial Feed
Z1-Z2 Diatoms (5,000cells/ml) + Rotifers (10 pieces/ml) NIL
Z3-Z6 Diatoms (5,000cells/ml) + Rotifers (10 pieces/ml) +Artemia nauplius (5pieces/ml) Microencapsulated Feed (30 microns)*
Megalopa 2nd Day Artemia (10 pieces/ml) Microencapsulated Feed (100 microns)*
Crab 1 2nd Day Artemia (10 pieces/ml) Microencapsulated Feed (100 microns)*
*commercial tiger prawn feed
*1used for production of blue swimming crab Portunus pelagicus

Culture media was changed at a rate of 30% daily, salinity and temperature of culture media was maintained at 30ppt and 29 °C respectively throughout the duration of the study. Survival was calculated daily by subtracting the number of dead larvae from the original population.
Results and discussion
From the larvae rearing trials carried a total of 9 C1 stage were produced from the total stocking of 3000 larvae giving a total percentage of 0.3 % survival to crab one stage. Mass mortality occurred during the Z1 to Z3 stage and also the megalopa stage. From the larval rearing trials it can be concluded that more studies need to be carried out on the larviculture of Charydis feriatus to discover the optimum requirements for the larviculture of this species nonetheless from it can be surmised that this species has good potential for mass production.

References:
1. Cowan L. (1985) Crab Farming in Japan, Taiwan and the Philippines, Queensland Department Of Primary Industries, Information series Q184009. 85pp

2. Cowan L. (1983b) Hatchery Production of crabs in Japan. In Proceedings of. 1st International Conference On Warm Water Culture Crustacea, 9-11 Feb. 1983 (Ed. By G.L Rodgers, R. Day & A. Lim). Brigham Young University, Hawaii.215-220
3. Edwards E. (1983) The Edible Crab and Its Fishery in British waters. Fishing News Books Ltd. Farnham, Surrey, England. 48-82.
4. Estepa P.F.D, Quinitio E.T and Rodriguez E.M Seed Production of the Crucifix Crab Charybdis feriatus SEAFDEC Bulletin July-September 2002(Vol. VII No. 3). 37
5. Kurata H. and Midorikawa, T. (1975). The larval stage of the swimming crabs P.pelagicus and P.sanguinolentus reared in laboratory. Bulliten Nansei Regional Fisheries Research Laboratory. 8:29-38
6. Lee D.O’C and Wickins J.F. (1992) Crustacean Farming, Blackwell Scientific Publications. 202,350
7. Ng P.K.L, (1999) FAO Species Identification Guide for Fishery Purposes,The Living Marine Resources of the Western Central Pacific, Vol 2 Cephalopods, Crustacean, Holothurians and Sharks (Edited by Kent E. Carpenter and Volker H. Niem), F.A.O Rome, 1045-1155
Here is a lab report on an experiment to obtain the optimum stocking density for Portunus pelagicus larvae

A picture of the Blue swimming crab

Optimal Stocking Densities for the Blue Swimming Crab Portunus pelagicus Larviculture

  Lirong Yu Abit,

Abstract

 

Larvae of the blue swimming crab  Portunus pelagicus(Linnaeus, 1766 ) were reared from hatching to first crab stage in laboratory conditions using 3 different stocking densities. From the study it was observed that a higher stocking density resulted in higher survival rates.

 

Introduction

 

 

Most of the large crab species (Brachyura) are edible, but the majority of commercial crabs are members of 3 families: Portunidae ( Swimming crabs), Xanthidae ( Mud crabs) and Cancridae ( Cancer crabs) ( Bardach et al., 1972). The blue swimming crab Portunus pelagicus (synonym : Neptunus pelagicus) is a commercial species found throughout  Indo-Pacific waters and is of  significant importance in fisheries of most countries located in that region.  To date there has been no large scale aquaculture of this species and this can be attributed to the lack of juvenile seed from the wild or hatchery for stocking. In Japan, Portunus trituberculatus has been bred for restocking in the wild but only a small percentage has been cultured to market size (Cowan , 1985). Experimental culture of Portunus pelagicus was tried at the Usa Marine Biology Station at Kyoko University with early optimism, but resulted in little success. The main problem with this species is cannibalism, with survival to first crab stage at only 10%. ( Bardach et al., 1972). Like other Brachyura, the eggs of Portunus pelagicus hatch as planktonic zoea. After four  zoeal stages the larvae emerge into a single megalopa stage and finally into the first benthic juvenile crab.

 

Objective

To determine the optimum stocking density for blue swimming crab (Portunus pelagicus).

 

Materials and Methods

 

Broodstock and larvae collection

 

Berried female crabs (200 – 350 grams)  are selected and purchased from local fishermen using gillnets, only active crabs with large egg mass are selected. Crabs are disinfected with formalin (50 ppm) for  30 minutes before being placed in spawning tanks. Spawning tanks consist of  0.5 tonne black fiberglass tanks with top cover and aeration. Treated seawater is filled in each spawning tank till half of it’s capacity and 100% water exchange is carried out daily until hatching occurs. Crabs are not fed at this period. After about 2 to 7 days the egg mass on each berried female should hatch out into swimming larvae. The hatching rate is volumetrically estimated and healthy larvae are separated from the rest. Healthy larvae are characterized by rapid swimming to the surface of the water column and strong photoreaction.

 

Experimental Design

 

Location of Study

The study was carried out at the Department of Agriculture (Inland Fisheries), Sematan during the months of August till October 2003.

 

Stocking Density

In this study 3 different stocking densities were used, 250 pieces of larvae per liter of water, 125 pieces of larvae per liter of water and 62.5 pieces of larvae per liter of water. Larvae were held in flat-bottomed HDPE containers of light blue color with a capacity of 50 liters.  Treated seawater of 20 liters was filled in each container. The study was carried out in a fully randomized design and 5 replicates for each experimental stocking density was used. Temperature was maintained at 29 °C in a temperature-controlled room.

 

Seawater

 

Before pumping raw seawater from the estuary, salinity was checked using a refractometer to make sure it is within the range of 29-31 ppt. The water was then pumped into 200-ton concrete tanks for setting and treatment with chlorine 25 ppt. The water was left to set for 24 hours before being dechlorinated with sodium thiosulphate of equivalent range. The water was then filtered through 100-micron muslin cloth bags to get rid of impurities and into 10 tonne covered holding tanks. Finally this water was once again treated with chlorine of 25 ppt and left in strong aeration for 24 hours before being dechlorinated with sodium thiosulphate of equivalent range. Only then was the water used for brood stock and larvae. Water stock temperature was maintained at 28°C and Dissolved Oxygen at above 10ppm. PH of water was within 8.0 for the duration of experiment. Water exchange of approximately 10% was carried out daily to get rid of excess food and waste ,during every larval stage water exchange of 30% was carried out to ensure that the water suitably clean.

 

Feed

 

Cultured mixed diatoms ( Chaetoceros  sp.  And Skeletonema sp.) cultured beforehand were fed to the newly hatched larvae after filtration using a 100 micron mesh net and collection a 50 micron collection bag. The results was then diluted in 100ml of treated seawater and fed to the larvae at 1ml per liter. The mixed diatoms were fed from day one of hatching till larvae reached the Z3 stage. Rotifers ( Brachionus sp.) cultured beforehand were fed along with the mixed diatoms starting from stage Z1 till larvae reached Z4 stage at a rate of 1ml per liter. Artemia ( Artemia salina ) nauplius hatched 12 hours beforehand were fed to the larvae starting from Z3 stage until the larvae reached Crab 1 stage at a rate of 1ml per liter. Artificial food (size100microns) was also given starting Z3 stage at a rate of 0.1 ml per liter till the larvae reach Crab 1 stage. Feeding was done once daily.

 

 

 

 

Table 1: Larvae rearing feeding regime

Larval Stage	Feed	Artificial Feed
Z1-Z2	Diatoms (5,000cells/ml) + Rotifers (10 pieces/ml)	NIL
Z3-Z4	Diatoms (5,000cells/ml) + Rotifers (10 pieces/ml) +Artemia nauplius (5pieces/ml)	Microencapsulated Feed (30 microns)*1
Megalopa	2nd Day Artemia (10 pieces/ml)	Microencapsulated Feed (100 microns)*
Crab 1	2nd Day Artemia (10 pieces/ml)	Microencapsulated Feed (100 microns)*

*1 Commercial Tiger Prawn Feed Brand name: Monodon (Thailand)

*Commercial Tiger Prawn Feed Brand name: Larval Feed AP100 (Thailand)

 

Samplings

Larvae stages, salinity and temperature are recorded daily to make sure that there is no drastic fluctuations. Survival is calculated daily by subtracting the number of dead larvae from the original population.

 

Statistical Analysis

 

Data for survival (%) was analyzed using one way Analysis of Variance (ANOVA) while differences between means were tested using Duncan’s Multiple Range Test (DMRT).  

 

 

 

 Results

 

Brood stock and larvae collection

 

A total of 5 berried female crabs were purchased for the experiment.  Data obtained from each brood stock crab is shown in the table 1.

 

Table 2: Brood stock Data

 

 

Stocking Density

 

A total of 5000 larvae were stocked in each container representing the stocking rate of 250 pieces/l, 2500 larvae for each container representing the stocking rate of 125 pieces/l and 1250 larvae for each container representing the stocking rate of 62.5 pieces/l.

 

Feed

 

Feeding was carried out daily according to the dosage stipulated in the methodology.

 

Salinity (ppt) and Temperature (ºC)

 

Salinity( ~30 ppt)  and temperature (~29 °C) remained stable due to the controlled conditions of the experiment. Fluctuations in both salinity and temperature were negligible and it is surmised that they did not contribute to the survival of larvae.

 

 

Survival rate

 

The survival of larvae was the highest in the stocking rate of 250 pcs/l followed by the stocking rate of 125 pcs/l and finally 62.5 pcs/l.  The mean percentage of survival in percentage for each of the stocking rates were 3.8% for the stocking rate of 250pcs/l, 3.48% for the stocking rate of 125pcs/l and 2.72% for the stocking rate of 62.5 pcs/l. Data on the percentage of survival can be seen in the table 2.

 

Table 3 : Percentage of Survival (%) of Portunus pelagicus larvae to Crab one stage in different Stocking Densities

 

 

Statistical analysis using ANOVA showed that F (at α = 0.05) differences between means were meaningful and further tests using DMRT showed that means of 250pcs/l and 125pcs/l were significantly different than the means of 62.5pcs/l.

 

 

Discussion

 

The higher stocking densities give a higher survival rate nonetheless more work should be carried out to confirm these findings.

 

References

 

1.      Bardach J.E, Rhyter J.H and Mclarney W.O (1972) Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms, Wiley Interscience, John Wiley & Sons Inc. 668-674

2.      Boxshall, Hooper & Williams (2000), Blue Crab, Fishery Assessment Report

3. Cowan L. (1985) Crab Farming in Japan, Taiwan and the Philippines, Queensland Department Of Primary Industries, Information series Q184009. 85pp

 

4.      Cowan L. (1983b) Hatchery Production of crabs in Japan. In Proceedings of. 1^st International Conference On Warm Water Culture Crustacea, 9-11 Feb. 1983 (Ed. By G.L Rodgers, R. Day & A. Lim). Brigham Young University, Hawaii.215-220

5.      Edwards E. (1983) The Edible Crab and Its Fishery in British waters. Fishing News Books Ltd. Farnham, Surrey, England. 48-82.

6.      Kangas M.I (2000) Synopsis on the Biology and Exploitation of the Blue Swimmer Crab, Portunus pelagicus Linnaeus, in Western Australia, Fisheries Research Report No. 121, 2000, Published by the Fisheries Research Division WA Marine Research Laboratories, Western Australia.1- 15

7.      Kurata H. and Midorikawa, T. (1975). The larval stage of the swimming crabs P.pelagicus and P.sanguinolentus reared in laboratory. Bulliten Nansei Regional Fisheries Research Laboratory. 8:29-38

8.      Lee D.O’C and Wickins J.F. (1992) Crustacean Farming, Blackwell Scientific Publications. 202,350

9.      Rahman,  M.N.A (1998) Kaedah Statistik, Penerbit U.P.M Serdang. 66-181