Grow mudcrab in ponds

aquafarm news • mudcrab culture

G row m udcrab in ponds

B y M C a s t a ñ o s Il l u s t r a t e db y E Ledesma Ph o t o s I Tendencia, M de los Santos

A Q D 's te c h n o lo g y v e rific a tio n te am h a s fie ld -te ste d m u d c ra b c u ltu r e . T h e tr ia ls w e re c o n d u c te d at the Jalan d o n i and M o n telib an o F arm s in EB M ag alo n a and at the G arga rita F arm in H im am aylan, N egros O ccidental.

B e lo w are the step s recom m end ed by A Q D in rearing m ud crab (S cy lla serra ta , S. o c ea n ic a ) in brackishw ater ponds.

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C H O O S E A SU IT A B L E SIT E . M ake sure m arine or brack ishw ater is sufficient year-round, relatively unpo llu ted or far from sources o f pollution. F resh­

w ater m u st be av ailab le particularly in summ er.

Site m u st be accessible and secured from p o a c h ­ ers. M u d crab grow best at 18-30 ppt and 25-30°C.

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C O N S T R U C T rectan g u lar p onds of sizes 5,000 to 10,000 m 2. A llow for 0.6 to 1.0 m w ater depth.

L e v e l the p o n d bottom . M ake the pond gates and dikes structurally strong and free of leaks.

C o n stru c t sh e lte rs o r sm a ll h id in g p la c e s for m udcrab; use saw ed -off bam boos or used PVC pipes m easu rin g 50 cm long w ith 15 cm diam eter o p e n in g . P lace th ese 'h id es' at strategic areas

around the pond. C anals or trenches are optio nal though these can serve as refuge for m udcrab and m ake h arvest and w ater ch ange easier. C atw alk s are also optional though these can help facilitate feeding, m onitoring, and stock sam pling.

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PREPARE T H E P O N D S . T otally drain the pond, dry for ~2 w eeks until the soil cracks, and rem ove ex traneou s species (fish, w eed s, o th ers). Treat undrainable areas w ith am m onium sulfate and quick lim e (1:5 ratio) at the rate o f 0.5 kg per m 2. A lter­

natively, use derris root (5% rotenone) at 0.5-2.0 g per ton o f p ond w ater or teaseed cake at 12 g per ton for <15 ppt or 20-30 g per ton for >15 ppt.

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INSTALL nylo n net fence using "A" net h av in g 1- 2 cm m esh close to the perim eter dike. Support the net fence vertically w ith bam boo or w oo d en posts and h orizo ntally w ith bam boo splits em bedded 50- 70 cm along the base. Install plastic strips or sheets (50 cm w idth) along the top edge of the net fence

A typical m udcrab pond. N ote that the nylon n et fen ce may not be necessary for relatively steep con crete dikes.

14 SEAFDEC Asian Aquaculture Vol . XIX No. 3 August 1997

aquafarm news • mudcrab culture

to p r e v e n t m u d c ra b from clim bing o v er the top.

In stall m o und s or used tires as additional shelters in the m iddle o f the pond, high enough so that the top portion re m a in a b o v e w a te r e v e n w hen the pond is flooded to its lim it (60-100 cm).

Stacked ru bber tires are used as shelters. K eep the top above water.

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G R O W N A TU R A L FO O D follow ing the plankton m ethod. Introduce at m o st 0.8 - 1.0 m w ater depth into the pond. C heck the screens at the pond gate to prevent entry of u n w anted species in the pond.

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STO C K M U D C R A B 1-2 w eeks after flooding. U se m udcrab ju v en iles w eigh in g 30-40 g or m easuring 5-10 cm carapace w idth. Stock 5,000 to 10,000 juveniles per ha.

N ote that m udcrab ju ven iles need to be nursed for 1- 2 w eeks in net cages if sm aller juveniles are stocked (1-2 cm carapace length). In the nursery, stocking d ensity is 120 ju v en iles per m 2. M udcrab juveniles are fed trash fish, A c e te s, or green filam entous algae ("lum ut"). C over the netcages w ith coconut fronds to serve as shelters and to increase surface area for attachm ent by crabs. Sort the stock every w eek, and stock the 5 cm ju v en iles in g ro w -o ut ponds.

In stocking n e w ly arrived ju v e n iles in g ro w -o u t ponds, acclim ate them first by sp rink ling pond w ater to the crabs p la ced in a b asin. D o this for 30 m inutes, or until the juveniles are com pletely subm erged. If the pincers are tied, cut the knots.

Do not cut the pincers.

R elease the ju v en iles even ly around the pond.

It's best to stock early in the m o rn in g o r late in the afternoon w hen it is cool.

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TA KE C A R E of the m ud crab stock by (a) re g u la rly c h a n g in g the w a te r (1 0 -3 0 % per spring tide cycle); (b) ch eck ing for leaks in the dikes and gates, and tears in the n etcages and fences; (c) feeding w ith ch opp ed trash fish, a n im a l h id e s / e n tra ils a n d s n a ils (g o ld e n kuhol). F eed at 10% then at 6% crab b ody w eigh t as culture p ro g resses; assu m e 100%

then 80% survival. F eed m ud crab tw ice a day, h alf of the food in the m o rning, h a lf in the afternoon. F eeding trays m ay be used; or feed m ay be broadcast.

SEAFDEC Asian Aquaculture Vol. XIX No. 3 August 1997 15

aquafarm news • mudcrab culture

Sam ple stock for gro w th once a w eek by using a bam boo trap ("bintol" or "taon"). M easure c ara­

pace len gth -w id th and body w eight. R ecord the m easurem ents.

A lso m o nitor w ater pH , salinity, tem pera­

ture, and w eath er condition daily.

M udcrab are fed tw ice a day.

A crab f a rme r and his bam boo crab trap.

8

H A R V E ST depend s on m arket dem and. Stock m ay be selectiv ely h arvested after 45-60 days.

M ud crab w e ig h in g 250 g and abo ve is n ot u n ­ com m on by this tim e. To harvest, allow th e stock to sw im ag a in st the current during spring tide.

Sco op out the b ig g e r or fatter crab u sing a scoop net. (O r u se net traps or "bintol" for selective h arvest.)

F at fe m a le crab h a v e m atu re g o n a d s or

"aligue" form ing underneath their carapace; fat m ale crab h ave m assiv e pincers.

T otal h arv est m ay b e done after 3-4 m onths (for S. se rra ta) o r 4-5 m onths (S. ocea n ica). Crab are h and -picked after totally d raining the ponds.

For more Information, contact

(Mr) Dan Baliao

Head, Technology Verification Project SEAFDEC Aquaculture Departm ent Tigbauan, Iloilo 5021

tel. 335 1009, 336 2937, 336 2965 fax 335 1008, 336 2891

e-m ail seafdec@ m ozcom .com tm s-seafdec@ phil.gn.apc.org

H o p in g for th e b est?

N oe D ellera, ow ner of a 40 ha fishfarm in the vicinity of the A m iliga n R iver in Pontevedra, Capiz, p o u rs o u t recent tales of woe. N ot su cceed in g w ith m ilkfish and tig e r shrim p culture ow ing to the lum inous bacteria, he relea sed n o t low er than 30,000 newly hatch ed mudcrab, king crab and native crab p e r p o n d (~13 ha co m p a rt­

m ents). E xp ectin g a h arvest in July, he has found ou t th a t the crabs w eigh ed le ss than

he expected. O ne of his p o n d w atchers a ttrib u tes the problem to the kind of so il the p o n d has. He thinks that the p on d s need to lie fallow, as th ese have been used constantly. -N J D

16 SEAFDEC Asian Aquaculture Vol. XIX No. 3 August 1997