The Snailfish

Just after noon, a scientist came up from the wet lab. He carried a glass jar with both hands. He set it carefully on a folding table in the shade. Polly hopped over.

Inside the jar, in clear liquid, was a small fish. It was about the length of Polly's wing. It looked soft, like a tadpole left too long in water.

She bent her head close, the small round lenses of her glasses bobbing slightly. The fish had a pale pink body, two dark eyes, and a small worried mouth. Its tail came to a thin point.

"This is Pseudoliparis swirei," the scientist said. "The Mariana snailfish. We brought it up from almost eight thousand metres down." He paused. "No fish lives deeper than this."

Polly tilted her head. The scientist explained: at that depth, the water presses on everything from all sides. The cells of a normal fish would crumple. The proteins inside the cells would stop folding the right way.

The snailfish has a special chemical inside its cells. The chemical is called TMAO. It works like a chemical brace. It stops the proteins from breaking under the pressure.

"But there is a limit," the scientist said. "Past eight thousand four hundred metres, even TMAO is not enough. Below that, no fish can live."

Polly thought about that. A line, eight kilometres down, drawn by chemistry. Below the line, no true fish. Only small soft creatures: shrimp-like amphipods, sea cucumbers, jellies.

The snailfish was small enough to slip past most predators. Its skin was thin, almost like a gel. It had no scales. It had no swim bladder, because a gas-filled organ would be impossible at that pressure.

It moved by waving its long body. Slowly, gently, in the dark.

The scientist held the jar up to the light. The body of the snailfish glowed faintly. "And until 2014," he said, "we did not even know what it looked like."

A whole creature, with its clever protein trick, and the world had simply not seen it. Polly looked at the small worried face. Eight kilometres below, others of its kind were going quietly about their lives.