The In-CRAB-able Courtship Ritual

Though fish and crab are obviously two different aquatic animals from their anatomy to the way they reproduce, they might still have something in common. Crabs court their perspective mates by building them a “temple,” whilst male fishes build their “nest”. Both are used to attract females and acts as substrates for hatching/laying of eggs. 

You'd think their odd body shape and rigid shells would make mating physically difficult. So just how do crabs do it? In order to grow and increase their size, crabs must first molt, or shed their exoskeleton. And it is only during this molting period — when the new shell hasn't yet hardened — that most aquatic crab species mate. 

Like most fishes, crabs do release pheromones too, however, varying on what specie of crab it is. For some specie like blue crab (Callinectes sapidus), the males release pheromones then use their claws to fan the scent towards prospect females. But in some species including Dungeness crab (Cancer magister), the female releases pheromones to draw roaming males. Crabs then engage in premating hug where the male crab will wrap its claws and legs around the female. Some female crabs will go into this position willingly. In some cases, the male must prove himself through the hug, and once she’s convinced he’s strong enough, she’ll stop struggling.

Sure enough, these crabs love cuddling with their mates. Unlike fishes’ brief courtship ritual, the crabs’ premating embrace lasts for several days! After which, the female will start molting and pair with the mate. 3The male transfers sperm by inserting his gonopods (sexual organs resembling antennae) into the two genital pores, called gonophores, on the female's underside. The female then will store the sperm in a storage sac called spermatheca  until she is ready to use it and fertilise the eggs. The male then will guard the female giving her shell time to harden before taking off in search of a new mate.