Shoal (The Underwater War)
From Tardis Wiki, the free Doctor Who reference
The Shoal were a fish species who communicated by colours of the skin as a sign of emotions. They lived in underwater cities. They were divided between the "low swimmers", the "medium swimmers" and the "high swimmers". The low swimmers had a white globe, which they could use to stun other Shoals or even kill them. The fish creatures had also fashioned a forked weapon as protection.
Their home planet was Hydron and the capital city of their planet was Reef. They used underwater roads to travel above the water beds. (PROSE: The Underwater War)