Robotuna.

What's shaped like a tuna, swims like a tuna, but transmits data to scientists on shore? It's Robotuna, an underwater robot designed to "swim" underwater longer than other robotic submarines.

Scientists often use these subs to map the ocean floor, conduct fish counts, and monitor pollution over time. But "you simply can't put enough batteries on board for long-term missions," says David Barrett, an ocean engineer at Massachusetts Institute of Technology (MIT).

So Barrett and his team decided to save fuel by making their robot propel itself more efficiently--like a fish.

Hence, Robotuna's design, which includes:

* a streamlined body, which cuts down on drag, the resistant force of water pushing against it, and

* a backbone of metal vertebrae, which bends in response to a motor's signal to "swish" the tail side to side for propulsion.

The sub now swims in an MIT tank, attached to cables so scientists can track its movements. This summer, the team hopes to release a free-swimming model into a pond, and soon, into the open sea.