66
If the enemy approaches, the blue crab gets a defensive position. Opens and
removes clamps. The legs are ready for side movement. Blue crabs also prefer live
food. Mussels and oyster beds are feeding areas of blue crabs. The other part of their
diet is dead fish, algae, and seaweed. The life of the blue crab is about 2 years. The
female can release a million larvae at a time. Shells do not grow. They regularly
change the shell to grow. This event is called moulting. During moulting, the outer
hard shell disappears. Underneath it forms a new soft shell and hardens. The moulting starts behind the crab eye, breaking the shell on both sides of the mouth and
spreading over the entire shell. This break opens the shell. Each time, the lost limb
grows a little larger until it is completely formed. Immediately after the shell is
changed, the crab gets water. With the minerals taken from the water, the shell hardens within 12–48 h. Soft crabs are usually found in June, July, and August; however,
they can be encouraged to change their shells in specially developed tanks. Thus,
the soft-shell season can be extended. Crabs are sold at high prices right after the
shell change (Dore 1991).
The male crab strolls over the female a few days before the female crab changed
its shell. These cases are called doubler. It protects female crab which is defenceless
and weakened during the moulting from external influences and harmful organisms.
Blue crabs love the brackish waters in summer and the ocean depths in winter.
Brackish water, mud and clayey lagoons and creeks are suitable for the growth of
blue crabs (Gokoglu and Oray 1997).
Portunus pelagicus (Linnaeus, 1758)
Carapace rough to granulose, front with four acutely triangular teeth; nine teeth on
each anterior lateral margin, the last tooth 2–4 times larger than preceding teeth.
Chelae elongate in males, larger chela with conical tooth at base of fingers. Colour:
males with blue markings, females dull green/greenish brown. It prefers sandy to
sandy muddy substrates in shallow waters down to a depth of 50 m, including areas
near reefs, mangroves and sea grass and algal beds. It is collected mainly by artisanal traps, trawls, beach seines, cylindrical wire traps, folding traps, pots, and drop
nets. This species is most widely sold in markets in Southeast Asia. It is distributed
throughout Indo-west Pacific (Ng 1998). It is a crab species that is included in the
Mediterranean ecosystem through the Suez Canal. This species has delicious meat
and high economic value (Fig. 2.10).
Scylla serrata (Forskal, 1775)
Carapace mouth, with strong transverse ridges; H-shaped gastric groove deep; relatively broad frontal lobes, all in line with each other; broad anterolateral teeth, projecting obliquely outwards. Well-developed spines present on outer surface of
chelipedal carpus and anterior and posterior dorsal parts of palm.
S. serrata prefers more oceanic waters, usually found just offshore on soft muddy
bottoms. All species of Scylla prefer soft substrates in shallow or intertidal water
and mangroves. They are collected by trawls, traps, baited wire mesh pots, hooking
and hand. Main markets are Taiwan, China, Hong Kong, and Singapore. They are
always sold for high prices. All four species of Scylla apparently have a wide IndoPacific distribution.
2 Crustacean Shellfish
If the enemy approaches, the blue crab gets a defensive position. Opens and
removes clamps. The legs are ready for side movement. Blue crabs also prefer live
food. Mussels and oyster beds are feeding areas of blue crabs. The other part of their
diet is dead fish, algae, and seaweed. The life of the blue crab is about 2 years. The
female can release a million larvae at a time. Shells do not grow. They regularly
change the shell to grow. This event is called moulting. During moulting, the outer
hard shell disappears. Underneath it forms a new soft shell and hardens. The moulting starts behind the crab eye, breaking the shell on both sides of the mouth and
spreading over the entire shell. This break opens the shell. Each time, the lost limb
grows a little larger until it is completely formed. Immediately after the shell is
changed, the crab gets water. With the minerals taken from the water, the shell hardens within 12–48 h. Soft crabs are usually found in June, July, and August; however,
they can be encouraged to change their shells in specially developed tanks. Thus,
the soft-shell season can be extended. Crabs are sold at high prices right after the
shell change (Dore 1991).
The male crab strolls over the female a few days before the female crab changed
its shell. These cases are called doubler. It protects female crab which is defenceless
and weakened during the moulting from external influences and harmful organisms.
Blue crabs love the brackish waters in summer and the ocean depths in winter.
Brackish water, mud and clayey lagoons and creeks are suitable for the growth of
blue crabs (Gokoglu and Oray 1997).
Portunus pelagicus (Linnaeus, 1758)
Carapace rough to granulose, front with four acutely triangular teeth; nine teeth on
each anterior lateral margin, the last tooth 2–4 times larger than preceding teeth.
Chelae elongate in males, larger chela with conical tooth at base of fingers. Colour:
males with blue markings, females dull green/greenish brown. It prefers sandy to
sandy muddy substrates in shallow waters down to a depth of 50 m, including areas
near reefs, mangroves and sea grass and algal beds. It is collected mainly by artisanal traps, trawls, beach seines, cylindrical wire traps, folding traps, pots, and drop
nets. This species is most widely sold in markets in Southeast Asia. It is distributed
throughout Indo-west Pacific (Ng 1998). It is a crab species that is included in the
Mediterranean ecosystem through the Suez Canal. This species has delicious meat
and high economic value (Fig. 2.10).
Scylla serrata (Forskal, 1775)
Carapace mouth, with strong transverse ridges; H-shaped gastric groove deep; relatively broad frontal lobes, all in line with each other; broad anterolateral teeth, projecting obliquely outwards. Well-developed spines present on outer surface of
chelipedal carpus and anterior and posterior dorsal parts of palm.
S. serrata prefers more oceanic waters, usually found just offshore on soft muddy
bottoms. All species of Scylla prefer soft substrates in shallow or intertidal water
and mangroves. They are collected by trawls, traps, baited wire mesh pots, hooking
and hand. Main markets are Taiwan, China, Hong Kong, and Singapore. They are
always sold for high prices. All four species of Scylla apparently have a wide IndoPacific distribution.
2 Crustacean Shellfish