In a food processor place the tomatoes and chop them to almost a puree consistency.
In a large heavy bottom pan place some olive oil and the garlic. Let the garlic golden, but not burn and remove when done and toss. Add the tomatoes puree and season with salt and pepper.
Cover and simmer for 30 to 40 minutes. Add the basil leaves as well as the Chilean Sea Bass, cover and cook until the fish is ready, another 5 to 10 minutes, or until fish is cooked to desired consistency. In a large pot, bring salted water to a boil and cook the pasta to desired doneness.
When the pasta is ready, drain well and place in a large platter. Put a tablespoon of butter and mix well. Add the tomatoes sauce and mix. In a large plate add the fettuccine and top it with the Chilean Sea Bass. Serve nice and hot.