Importance of fish in diet

I truly believe that eating fruit is one of the most natural diets to take on. I plan on being fruitarian for a while, and then become raw vegan. However, there is the theory that our evolution was only able after eating fish. Here's an article that describes it more:

http://www.medicalnewstoday.com/medicalnews.php?newsid=38009

Also, the Okinowans of Japan are said to be the healthiest most long-lived people on earth, with a diet mainly in fish.

Can anybody argue against the importance of fish in our diet? I know that it is parasitic and second hand food (as is all meat) but it seems to have many benefits that aren't obtainable from only fruits.