There are an asortment of UW/Amphibians in 101 Life Forms (BITS), a spplement for GT, but useable by any Traveller flavor with some work..
JTAS -16, 1983 "Contact-Githiasko!"
pp12-14, &27. a race of intelligent sophonts from coreward edge of he Imperium whose homeworld is Githiaski/Antares (2406).
J. Andrew keith, author.
(They're cephalopods-Squids of sorts!)
(does the WB-kids double take!#@!)-Are you the rreal Trader Jim? Nawwwwwwwwww, couldn't be!