The mangrove killifish (Rivulus marmoratus) is quite an odd fish — and not just because it can breed without a mate. Scientists recently discovered that it can live inside trees, out of the water, for several months each year. The mangrove killifish can actually change its biology and metabolism so that it can breathe air and live out of the water.

Normally found living in the mangrove swamps of Latin America, Florida and the Caribbean, this killifish can flop its way to the temporary housing of rotting branches and tree trunks when the water dries up around the mangroves.

Researchers discovered hundreds of these normally aggressive fish packed into the tight quarters of rotting logs. Temporarily suspending their aggression, these fish were lined up mouth to tail down the length of paths carved out by insects.

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