Good
review of fish oil.
DHA is vital for brain function, controlling inflammation, keeping depression at bay, etc. I think it's a vital part of any therapy and not just UC.
As for the sources, I know only of one good and reliable brand that works for me and that's Nordic Naturals. I would get the rest from the low mercury fish like sardines, anchovies, salmon 2-3x a week.
Hope this a helpa!