Greenfish's shakedown cruise 22 July to 13 September 1946, took her to Barranquilla, Colombia; the Canal Zone; Callao, Peru; and St. Thomas, Virgin Islands.

Various exercises along the American coast and in the Caribbean occupied Greenfish until 8 January 1948, when she entered the Electric Boat Co. yards for a GUPPY II conversion.

Returning to New London 21 August 1948, Greenfish sailed on her "second" shakedown cruise 1 September, with Rear Admiral James J. Fife, Commander, Submarine Force, Atlantic Fleet, aboard.

Greenfish entered Pearl Harbor Shipyard 15 December 1960 for a FRAM (Fleet Rehabilitation and Modernization) overhaul and extensive conversion to a GUPPY III class ship.

In addition to special operations, the submarine participated in various fleet and ASW exercises and visited several ports, including Hong Kong, Manila, and Okinawa.

Returning to Pearl Harbor June 1962, Greenfish engaged in local operations until October, when the Cuban Missile Crisis sent her to Japan to strengthen the 7th Fleet.

Upon return to Hawaii December 1962, she underwent a brief overhaul and then resumed her peace time schedule of local and special operations interspersed with training exercises.

Greenfish was decommissioned, struck from the US Naval Register 29 October 1973, and transferred (sold) under terms of the Security Assistance Program to Brazil, 19 December 1973, where she was renamed Amazonas (S-16), the eighth Brazilian Navy ship to be named for the Amazon River.