Darwin the dolphin - Talking bottle-nose dolphin on the sci-fi series SEAQUEST DSV/NBC/1993-95.

Ensign Darwin lived aboard the 1,000-foot SeaQuest Deep Submarine Vehicle (he had his own tank). Darwin communicated via an electronic device that interpreted his clicks and whistles into a squeaky human voice.

Darwin was originally brought onboard by the ship's Captain Nathan Bridger (Roy Scheider) who designed the submarine to include corridors with water-filled tubes running along them just above head level for Darwin to make his way around the vessel. When Darwin goes on missions outside the sub he wears his own breathing apparatus.

Darwin's favorite crew member was teenage techno-genius, Lucas Wolenczak (Jonathan Brandis).

Animal rights anti-captivity groups such as the Florida based group The Dolphin Project were happy to discover that Darwin was not a live mammal but rather a mechanical one, although real dolphins were used on the set and did appear on the show. (See - "If Dolphin's Could Talk" interview in TV Guide 10/23/93 p. 37).  

"The 21st Century...Mankind has colonized
the last unexplored region on Earth...The oceans. 
 As Captain of the seaQuest and her crew, we are its guardians
...For beneath the surface ...Lies the Future."
--Captain Nathan Hale Bridger