The ridged swimming crab is named aptly because of the distinctive ridges on the dorsal side. Swimming crabs are distinguished from walking crabs by the presence of paddle-shaped last pair of legs that can be rotated like propellers of a boat engine to swim well in all directions.
Charybdis (natator) natator is characterized by brown to orangish colouration on the upper surface (dorsal side) while the under surface (ventral side) is found to have a bluish colouration, mottled with white and pale red. Legs are dark and reddish brown in colour. The carapace is densely covered with short pubescence (covered with short soft hair; downy) and is absent on the distinct transverse ridges in the anterior side. There are six spines on the sides of the fan-shaped carapace.
The ridged swimming crab has eight rounded small rounded lobes structured between the eyes which are not far off from each other. Body has fine hairs that assist in trapping sediments. At the tip of the pincers there is a distinct black tipped with blue spotted colouration. The bright blue colouration is also noticed at the base of the claw.
Charybdis (natator) natator occurs in depths ranging from 5 – 40 m inhabiting rocky-sandy substrates or near reefs. These crabs prefer to hide under stones of sandy shores. They are distributed in the Tropical and Subtropical climatic regions.
Top of Form
The maximum size of the crab based on carapace length (Shell length) is 17 cm while the minimum is 5 – 7 cm. Its distribution ranges from East Africa, Madagascar, Red Sea, India, China, Japan, Philippines, Thailand, Malaysia, Singapore, Indonesia and Australia.
The ridged swimming crab is not a major fishery in India and is only fourth to the other three economically important species namely Portunus pelagicus (the blue swimming crab), Portunus sanguinolentus (the three spot crab) and Charybdis feriata (crucifix crab). It is harvested by specially designed gears called as crab nets (bottom set gill net) that are operated in shallow depths near reefs or sandy areas. They are also obtained as by-catch from bottom trawling operations. Locally, the crabs are sold depending on size for prices 180 – 250 (Indian Rupee).
Fishermen and folks who are in love with seafood will not refuse a dish prepared from the ridged swimming crab!
Subgenus: Charybdis (Charybdis)
Author: (Herbst, 1794)
Not Assessed (NA)
© Deepak Samuel, February 2014