I done a little looking around and I seem to find some difference of opinion on this matter- some web sites claim :
Tilapia - Saint Peter's Fish
• Native to Africa and the Nile River Basin in lower Egypt
• Omnivore [eats organic material, not other fish]
• Breeds prolifically indoors or outdoors in small areas
• Healthy [low fat - low calorie]
First fish taken into space [with astronaut John Glenn in 1998] READ MORE >>
Why Tilapia?
Morning Star Fishermen (MSF) chose Tilapia for MSF's aquaculture program because they are hardy fish that like warm water, can thrive in fresh, brackish, or salt water, and have excellent tasting, firm, white meat. The fish also has a unique history and a surprisingly rare combination of qualities that are found in few other fish.
The Genus Tilapia
This Tilapia is endemic to warm waters throughout the world. The aquaculture, or fish farming, of Tilapia is recorded in human history as far back as ancient Egypt. Tradition holds that the Tilapia was the fish that Jesus used to feed the five-thousand on the Sea of Galilee - thus one of its common names, "St. Peter's Fish." Tilapia is also referred to as "The Wonder Fish" and "Nile Perch."
He instructed Peter to "go to the lake and throw out your line. Take the first fish you catch; open its mouth and you will find a four-drachma coin. Take it and give it to them for my tax and yours." (
Matthew 17:27) According to tradition this is a species of fish called the chichlid, or Tilapia galilaea. It has a large mouth, a long dorsal fin which looks like a comb and can be up to 1.5 feet long and 3 pounds in weight. It is found on restaurant menus in Tiberias under the name "St. Peter's Fish" (above right).
Others seem to support your claim about it being an exclusively saltwater fish
here are some links:
http://www.morningstarfishermen.org/fish.html
http://www.welcometohosanna.com/LIFE.../ministry3.htm