The classic eating crabs. Seafood is fresh is Thailand and popular, we normally barbecue the crab and pick them apart to eat, but for some dishes you need to prep the crab by removing the meat and any egg roe it has.
Male crabs have more meat in the body, female crabs have less meat, but also have red egg roe, which is a more concentrated crab flavor.
(See after the break for how to determine the sex of a crab and how to prep it).
Firstly, sexing the crab. Turn it over. Looking at the underside, you can see how different male and female are on the underside of the shell. The female (at the top of the photo) has a sort of wrapped over rounded section, the male has a more pointed section of shell there that's a tighter part of its shell.
If you want egg roe, obviously you choose the female, but choosing a female is no guarantee of getting roe.