The weird and won­der­ful world of the clown fish

It’s hard be­ing a clown fish. You’ve got kids to keep an eye on, ra­zor-sharp coral to watch out for and dan­ger­ous preda­tors at ev­ery turn. Oh, and there’s the small mat­ter of a sex change just around the cor­ner

World of Knowledge (Australia) - - Contents -

Don’t be fooled by the colour­ful scenery: it’s a tough life in amongst the coral reef! There’s danger ev­ery­where you look – some of the coral has ra­zor-sharp teeth, oth­ers are armed with deadly blades – while preda­tors con­stantly pa­trol the sur­round­ing wa­ters. It’s a world of con­trasts: the pret­ti­est-look­ing plant con­tains some of the most fa­tal neu­ro­tox­ins.

To sur­vive here as a small fish you’ll need nerves of steel, re­li­able al­lies – and a re­ally good plan. Luck­ily, the clown­fish has all three of these qual­i­ties. It spends its en­tire ten-year ex­is­tence slap bang in the mid­dle of the sea anemone, one of the reef’s most poi­sonous plants. Theirs is a sym­bi­otic re­la­tion­ship, ben­e­fi­cial to both part­ners: the toxic ten­ta­cles of the anemone pro­tect the clown­fish from preda­tors, while in re­turn the colour­ful fish pushes its host some­thing nu­tri­tious ev­ery now and again and keeps its ten­ta­cles clean.

So that it doesn’t fall vic­tim to the deadly ten­ta­cles, the clown­fish fa­mil­iarises it­self with them by gen­tly brush­ing against the ten­ta­cles sev­eral times. The fish then coats it­self in mu­cus so that the sea anemone doesn’t see it as an in­truder. In ef­fect, the clown­fish is say­ing, “I be­long to you, I’m harm­less, there’s noth­ing to eat here.”

In the cen­tre of the sea anemone, Mr Nemo watches over 1,000 eggs ev­ery day. That’s right, Mr Nemo – with clown­fish, it’s the men who look after the kids. They’re also an in­te­gral part of a plan that is as in­ge­nious as it is unique: clown­fish be­lieve in a size-based hi­er­ar­chy – big is best. In prac­tice it looks like this: the male fish all re­port to a lone, large fe­male. The breed­ing male is sec­ond largest in the group, and the oth­ers get pro­gres­sively smaller as the hi­er­ar­chy de­scends. All live to­gether on a sea anemone. As soon as a fish dies, the sur­vivors move up the ranks by one po­si­tion. If that fish is also the fe­male, the breed­ing male changes sex and as­sumes the man­tle of leader. The largest non-breeder then be­comes the breed­ing male and so on. Com­pli­cated? Not re­ally. You just need to re­mem­ber that with clown­fish it’s al­ways the fe­male that rules the reef…

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