Isso é " Shards " de Brian Aldiss. Os protagonistas são transformados em criaturas de peixes para combater alienígenas aquáticos.
“The security of the world demanded this drastic experiment. The alien ship ‘landed’ a year ago in the North Atlantic, off Bermuda. Our submarines have investigated its remains on the ocean bed. They have found proof that the ship landed where it did under control, and was only destroyed when the aliens left it.
“The aliens were fish people, aquatics. The ocean is their element, and undoubtedly they have been responsible for the floods extending along the American and European seaboards and inundating the West Indies. Undoubtedly the popular press is right to claim we are being defeated in an alien invasion.” “My dear Roberts, I don’t doubt they’re right, but –”
“There can be no buts, Dr Collison. We’ve failed to make any contact with the aliens. They have eluded the most careful submarine probes. Nor is there any ‘but’ about their hostile intent. It seems more than likely that they have killed off all the eel family in some unimaginable slaughter under the Sargasso Sea. Before they upset our entire oceanic ecology, we must find them and gain the information about them without which they cannot be fought. Here are our spies, here in this tank. They have post-hypnotic training. In a couple more days, when they are fit, they can be released into the sea to go and get that information and return with it to us. There are no buts; only imperatives in this equation.”
Slowly the two men descended the metal stairway, the giant tank on their left glistening with condensation.
“Yes, it’s as you say,” Collison agreed wearily. “I would so much like to know, though, the insane sensations passing through those shards of human brain embedded in fish bodies.”