Western clownfish (anemonefish)
These fish live in a mutually symbiotic partnership with anemones.
While most fish avoid anemones because of the stinging cells in their tentacles, the clownfish is coated with protective mucus, which enables it to swim freely in and around the anemone.
In this way the clownfish is protected from predators and in turn, the clownfish protects its host anemone from butterflyfish and other predators that eat anemones. They keep the anemone free of dirt and debris.
While most sea creatures avoid anemones because of the stinging cells in their tentacles, pairs of clownfish live closely with anemones in a mutually beneficial partnership – which can last a lifetime!
Anemones have poisonous barbs in their tentacles, which fire on contact, injecting poison into their prey. To protect themselves, anemones secrete a slime that prevents the stinging cells on one tentacle from firing when they come into contact with other tentacles, or with the anemone’s body!
Clownfish have to trick the anemone into accepting them by darting amongst the tentacles until they have covered themselves with enough protective slime from the anemone.
Once protected by the slime, the clownfish are able to swim freely in and around the anemone. In this way they are protected from predators. The clownfish protect their host anemone by aggressively chasing away butterflyfish and other predators that eat anemones.
Sex change – the best of both worlds
Many fish have the ability to change sex. This is a strategy to maximise reproductive output. Some change from male to female while others change from female to male.
On coral reefs sex change from female to male is the dominant reproductive style. On these reefs there is intense competition for the best spawning sites and large dominant males set up territories that are defended against all other males. The larger the male, the bigger his territory and the more females he will attract to spawn with. In this way millions of eggs can be fertilised by a single male. Smaller fish cannot compete for these sites so they remain female until they are large enough to compete and the opportunity arises.
In contrast to this, clownfishes change from male to female! Why would they do this? Simply, there are two reasons:
• Lifestyle – there is only space for two adult clownfish per anemone and the bigger the female, the more eggs she can produce (small males can fertilise all these eggs easily).
• Eggs - unlike other reef fishes, clownfishes do not release their eggs into the currents to drift away. They attach them to the rocks under the mantle of the anemone, where they are protected while they grow.