Creatures of the Abyss by Murray Leinster

Excerpt:
He moved away along the deck. Terry went close to the side rail. A few minutes later the startling glare of one of the side searchlights smote upon the water away from the incredible scene. It moved slowly back and forth. Where the light struck, the sea seemed totally commonplace. No fish could be seen. Then the white beam swept here and there in jerky leapings. There was nothing unusual on the surface, nothing beyond the limit of brightness, where the sea turned dark.

Deirdre said at Terry's side, "We didn't really expect this! I'm going to get a sample of the water, Terry. Want to help?"

She ignored his haughty withdrawal of the afternoon, and he could not stand on his dignity in the presence of such an incredible phenomenon. She got a water bucket from the nearby rack. A wave sprung up as she tried to fill the bucket overside. It touched her hand and she cried out. Terry jerked her back by the shoulder. The bucket bumped against the Esperance's side, hanging on the line attached to the rail.

"What's the matter?"

"It stung! The water stung! Like a nettle!" Shaking a little, Deirdre rubbed her wet hand with the other. "It doesn't hurt now, but it was like a stinging nettle—or an electric shock!"

Terry hauled in the bucket and set it down. He leaned far over the rail. He plunged his hand into a lifting pinnacle of the sea. Instantly, his skin felt as if pricked by ten thousand needles. But his muscles did not contract as they would in an electric shock. The sensation was on the surface of his skin alone.

He shook his head impatiently. He put his finger in the bucket he'd lifted to the deck. There was no unusual sensation. He dipped overside again. Again acute and startling hurt, from the mere contact with the water.

Deirdre still rubbed her hand. She said in a queer, surprised voice,

"Like pins and needles. It's like—like the fish-driving paddle! But worse! Much worse!"