Pay special attention to those orange spots on the anal fin.

Astatotilapia burtoni

(via Kevin Bauman)

Those spots help this fish get oral sex.

As is the case in many fish species, the sight of a brightly coloured male somehow triggers females with ripe eggs to start releasing them. But in cichlids, there is a twist. Females hold their eggs in their mouths and incubate them there after fertilisation – a behaviour that is thought to have evolved to protect the eggs from predators.

As soon as a female has spawned her eggs, she collects them up in her mouth. Normally, sperm released into the water by a male nearby will then fertilise the eggs.

But males of certain cichlid species in east Africa have evolved a way to increase the odds that females take up their sperm. Oval yellow markings resembling the eggs are found on the anal or pelvic fins. When a female approaches the male, she thinks she sees an egg on its fin, so tries to vacuum it up in her mouth – and get a mouthful of sperm from the canny male in the process.

That fish may think it’s come up with a clever trick, but the Catholics know it’s going to fry.