Presented by- Jyoti SarojDepartment - Fisheries Resource ManagementCollege of Fisheries, Veraval, Gujarat

* EMBRYONIC DEVELOPMENT OF BLUE SWIMMER CRAB(Portunus

pelagicus)

Introduction*It is one of the major marine crab species landed in India. *It is distributed throughout Indian coast.*It is also called as blue swimmer crab. *Crabs are mainly caught in bottom trawl nets.*Three species Portunus trituberculatus (Japanese “gazami”), P. pelagicus (“blue swimming crab”) and Callinectes sapidus (“blue crab”).

Global catch of Portunus pelagicus during 1963-2010

Scientific Classification of Portunus pelagicus

Kingdom- AnimaliaPhylum- ArthropodaSubphylum- CrustaceaClass- MalacostracaOrder- Decapoda Infraorder- BrachyuraFamily- PortunidaeGenus- PortunusSpecies- pelagicus

Distribution*Red sea, Mediterranean, East coast of Africa, Persian

Gulf, Pakistan, India, Sri Lanka, Singapore and Philippines to Australia, New Zealand, China and Japan.

*Marine crab seed is not easily available from the wild and it should not be collected from the wild for the sake of conservation.

Morphology

Biology*Sexes can be easily differentiated.

* Male crabs are bigger than the females with a dark-blue carapace, pale belly and rich blue on their legs and claws. But female crabs are dull brown in colour.

*Male has pleopods modified as copulatory organs on the first and second abdominal somites.

*In the case of females the first four abdominal somites carry pleopods.

Cont..

*Size at first sexual maturity

50% of the female crabs attained sexual maturity when they

reached the size of 9.1-9.5 cm CW. 50% of the male crab’s

attained sexual maturity when they reached the size of 9.5-

10.0 cm CW.

Male and Female

Mating Behaviour*Most blue swimmer crabs mate in autumn.

*The males moult first. A courting male then catches a female and carries her beneath him for 4 to 10 days while fending off other males. The male helps the female to moult and then turns her over to mate while she is still soft-shelled. After mating, he continues to carry her around and protect her for another three-to-four days while her shell hardens.

* A male may mate with several females during one season.

Various Positions of Mating Behaviour

Pre Moult Guarding Moulting

Moulted shell

Pre Copulatory Guarding Male try to rotate the female

Mating

Post Copulatory Guarding spawning

Newly Spawned female

Spawning*Spawning was pronounced during January-February and

in September.

*The occurrence of mature, spent and berried crabs of P. pelagicus in large numbers during peak breeding season in the shrimp trawlers.

*The fecundity rate of P. pelagicus was ranging between 9,00,000 to10,00,000 eggs.

Ovarian Development Stage

*Stage 1 (Immature) *Stage 2 (Early maturing) *Stage 3 (Late-maturing) *Stage 4(Fully mature)

Eggs colouration and egg size during embryonic development

Egg fertilization stages

Colour of eggs Egg size(mm)

Max. Min.

Stage 1 Yellowish orange 0.436 0.208

Stage 2 Brown 0.472 0.296

Stage 3 Black 0.575 0.337

Egg Colouration During Embryonic Development

Stage 1 embryonic development with yellow-orange colour eggs

Stage 2 embryonic development with brown colour eggs

Stage 3 embryonic development with black colour eggs

Eggs at the time of oviposition

*Stage I – Blastula

*Stage II – Gastrula

*Stage III – Eye placode

*Stage IV – Pigment

*Stage V – Heart beat

Hatching of Zoea*One berried mother is introduced in a single hatching

tank.*Anticipating the hatching during the following night

mixed phytoplankton dominated with Chaetoceros spp.(10000 cell/ml) and rotifers (5no. /ml) are added in the hatching tank.* Hatching takes place during early morning hours. After

full hatching mother crab is removed.*In hatching tank aeration is stopped for few minutes.

Larval Rearing*1-5 ton capacity fibreglass tanks are generally used.

*Filtered seawater is used. The newly hatched active zoea are stocked in the larval rearing tanks with Stocking density of 50,000 no/t.

*Every morning 30-40% of the culture tank water should be exchanged.

*During the process tank bottom should be cleaned, excess feed and dead larvae must be removed using suitable filter after stopping the aeration.

Cont..Parameter Range

Salinity 30-33ppt

Temperature 27-310C

pH 8.0-8.5

Dissolve oxygen 4-8 ml/l

Total ammonia <0.1 ppm

Nitrite <0.05 ppm

*Life Cycle

Different Larval stages*First zoea-*Carapace length-0.44-0.54mm*Abdominal-telson length-1.07-1.23mm

*Cont..*Second Zoea-*Carapace length-0.72-0.77mm*Abdominal-telson length-1.46-1.54mm

Cont..* Third Zoea-*Carapace length-0.79-0.87mm*Abdominal-telson length-2.02-2.21mm

Cont..Fourth zoea*Carapace length-0.98-1.06mm*Abdominal-telson length-2.61-3.03mm

Cont..Megalopa-

*Carapace length-1.69-1.81mm*Abdominal-telson length-3.0-3.2mm

*Food and Feeding*Larval food for different stages and their feeding concentration in

the rearing water is given in the table.

Stage Food Concentration

Zoea I Chaetoceros + rotifer 25,000/ml + 40/ml

Zoea II Rotifer + Artemia 20/ml + 5/ml

Zoea III Artemia 5-10/ml

Zoea IV Artemia 5-10/ml

Megalopa Moina/Artemia + prawn-egg

custard

3-5/ml + 20-25mg/l

Crab 1-3 Prawn-egg custard 20% of the biomass

References-*Josileen Jose(CMFRI), Seed production and farming of blue swimmer

crab Portunus pelagicus*Jones, D. & Morgan, A Field Guide to Crustaceans of Australian Waters.*Yearsley, G.K., Last, P.R. & R.D, Australian Seafood Handbook,an

identification guide to domestic species.*Research Article- Mating Behaviour of Sand Crab, Portunus pelagicus

(Linnaeus), Soundarapandian P, Varadharajan D and Anand T*P. Soundarapandian and T. Tamizhazhagan, Embryonic Development of

Commercially Imporatant Swimming Crab Portunus pelagicus *Soundarapandian P*, Varadharajan D and Anand T, Mating Behaviour of

Sand Crab, Portunus pelagicus *Fisheries Fact Sheet, Published march 2011