Fish Oil definitely works! I'm taking 3000mg a day and I've only been diagnosed with severe UC a month ago, I've been doing great and I think its helping. Ofcourse I love all kinds of fish and if it werent for high levels of mercury I would eat every fish I could on a daily basis! Fish = anti inflammatory. But its not like a drug and doesnt work overnight, you're not all the sudden going to see results in 3 days... it's a natural supplement.
My Uncle is a health fanatic (he does not have UC or any other health issues), and was recently telling me about
mercury levels in different fish. Now, I don't remember which he said was better than the other, but either Pacific-caught fish are better than Atlantic, or vice-versa.
Here is a site explaining which fish you can without worry of mercury levels: http://www.healthlinkbc.ca/healthfiles/hfile68m.stm
Search around and you will find plenty of other resources regarding this matter.