To help raise money for the Extra Life charity, WotC has released a 39-page PDF adventure called Locathah Rising, which also includes the locathah as a playable race. Locathah are fish-people. You can pick it up for $9.99.
I get the feeling this is gonna be Grung-like in the "There are technically stats for this but we have not really bothered about anything outside of the one adventure" style because that's a bit of a big thing to deal withSuffocating after 4 hours on land is pretty limiting for a character.
+2 STR, +1 DEX, Natural Armor 12+DEX, Proficiency in Athletics and Perception, Advantage on saves vs charmed, frightened, paralyzed, poisoned, stunned, or put to sleep, must be submerged every 4 hours or you suffocate (eeep!), 30 ft walk/swim.
Suffocating after 4 hours on land is pretty limiting for a character.