Coastal Aquaculture and Mariculture (2+1)

Unit 2 - Traits of important cultivable species

2.9. Crabs

Among marine crustaceans, crabs rank third in their importance as gourmet food and the value of fishery they support after shrimps and lobsters.
Out of the 16 species of the crabs exploited through capture fisheries, Scylla tranquibarica and Scylla serrata are the larger ones attaining sizes of 0.5 to 2.0 kg and suitable for culture. They are known as mud crabs, green crabs or mangrove crabs. Both these crabs co-exist in the inshore sea, estuaries, backwater, coastal lakes and mangrove swamps of all maritime states of India, Andaman and Nicobar Islands. They prefer muddy and sandy bottoms. They breed in the sea and migrate to the estuaries, megalopa onwards. Males are bigger than females of the same age. They are omnivores feeding on shrimps, bivalves and fish among other food items. They are continuous breeders with peaks at different times in different places.

Scylla tranquibarica
This is the larger of the two species growing to a maximum size of 2.0 kg. Free living unlike S. serrata which burrows into the substratum.
Outer margin of carpus of chelipeds with 2 sharp spines. Colour of upper surface of body light to dark green. Polygonal marking on all walking and swimming legs.

Scylla serrata
Outer margin of the carpus of cheliped with one blunt spine. Colour of the carpapace greenish brown to ferruginous brown. No polygonal markings on legs. Lower surface of the fixed finger of cheliped dark to pinkish red in colour.