Fish are streamlined for propulsion.
Their bodies create little friction between them and the water that supports them. Light filters down from the water’s surface where we watch them take graceful turns around their tank’s curves.
In another tank, jelly fish, have their tentacles shown off by back lights.
The jelly fish are transparent, catching food in their tentacles and letting themselves be propelled by currents or by ingesting water and spitting it out to move in the direction of their prey.
They are other worldly.
Living without a backbone takes friction out of your life and floating in ocean currents is more healthy than fighting them.