Fish dominate the planet’s waters. They are the most varied and diverse back-boned creatures on the planet – and they need to be.
Sea and fresh water contain habitats that are more varied and tougher to live in than those on the land.
The peculiar variety of the fish world is exemplified by the weedy sea dragon. It looks more like a stray bit of sea weed. It moves by beating nearly invisible fins. Its breeding defies expectations. The female lays her eggs onto the male’s tail and he carries them about for two months. When they begin to hatch he shakes his body to help them free of their egg cases.
Not all fish abandon their young. The convict fish shares a network of tunnels with its offspring. Much of its life is a mystery – no one has ever seen a parent leave its burrow. But its thousands of young feed out on the reef on plankton, returning to the safety of the tunnels at night.
The Hawaiian goby makes an immense effort to find the right place to breed. The fish swim from the sea to the base of a huge waterfall. The churning water here is a tough place to live but hundreds of feet up at the top are secluded, still pools. The wall of rock looks impassable yet the gobies climb, sticking to the rock face with a specialized disc. Many die in the attempt but the few that make it find perfect breeding conditions.
Flying fish lay their eggs on flotsam such as palm fronds. When the fish begin to lay their strands of eggs, they work so fast that some are trapped and entombed. Eventually the whole thing becomes so heavy that it sinks to the safety of the sea bed.
As if the water doesn’t provide enough challenges the Japanese mudskipper is exposed on land when the tide retreats from the mudflats. It’s hard to be spotted by a mate in a two dimensional habitat, so the males leap to be seen. When rival males encroach on each others’ territories they fight by flipping and leaping.
The variety of challenges life in water poses are solved by fishes’ equally wide variety of behaviors. The jack gets rid of parasites by rubbing up against the rough skin of its greatest predator – the shark. Sailfish are the fastest fish in the oceans, quick and agile enough to knock individual sardines out of a shoal. Barbel follow hippos, waiting for them to defecate – a feast for the fish.
The immense range of fish strategies allow them to dominate the oceans – the one place on Earth humans have failed to make their own.