Twoline Cardinalfish

It lives in this sea and nowhere else, which is unremarkable here and would be extraordinary anywhere else.

Something like one fish species in seven in the 🌊 Red Sea is found only in the 🌊 Red Sea, a rate that is among the highest of any tropical sea and far above the rest of the 🌊 Indian Ocean. The reason is the shape of the place. The 🌊 Red Sea is a long, narrow, nearly closed basin joined to the rest of the ocean through one shallow, narrow strait at Bab el-Mandeb, and during the ice ages, when sea level fell by more than a hundred meters, that connection came close to shutting entirely. What was inside was isolated, in water that got hotter and far saltier than anything outside, and what survived came out the other side different.

So the fauna here is not just a subset of the 🌊 Indian Ocean's. It is a subset that was locked in a room and left to change, repeatedly, and the endemics are the result.

This one is a small translucent cardinalfish with two fine dark lines, in groups close to coral in shallow sheltered water, and it is one of roughly a hundred and fifty fish species that exist here and nowhere on earth.