How do fish and snakes have sex ?

Both fish and snakes have a single opening, called the cloaca, through which they excrete, mate and lay eggs/give birth. Most fish reproduce using external fertilisation. This means that the female lays her eggs, and the male then covers them with sperm in order to fertilise them. The young, called fry, will then hatch after an incubation period. There are a few exceptions - male sharks have two external reproductive organs called claspers, one of which is inserted into the female's cloaca and sperm delivered to the eggs whilst they are still inside her.

Some sharks then lay the eggs, whilst others retain them inside their bodies until the young are fully developed, when they are expelled. In seahorses, and their relatives the pipefish and seadragons, the female lays her eggs into a brood pouch on the male's belly.

Here, he fertilises them and keeps them until they hatch, when the tiny babies emerge from the pouch. Male snakes have two penises, often called hemipenes, which are usually kept inverted inside his cloaca. When he mates, they are everted, and one is inserted into the female's cloaca, delivering the sperm inside her.

It fertilises her eggs, which are then either coated in shell and laid, and will hatch after an incubation period (this is called being oviparous), or retained inside the body, without shells, until the young are fully developed and expelled from the mother's cloaca (this is called being ovoviviparous). Pythons and cobras are examples of oviparous snakes, and boas and rattlesnakes are examples of ovoviviparous ones