I've eaten at PassionFish three times. In my opinion, it's the best restaurant in the Reston/Herndon area. It's a formal place, with top notch service and excellent food. But it's expensive. Fortunately someone else was paying the three times I've eaten there.
The menu changes so I'm not sure how useful it is to mention particular dishes. However, my first visit featured something called Captain Crunch Sushi. It was beyond! The last time I visited, my 15 year old daughter thought she was in heaven when they brought her a side dish of lobster mac-n-cheese. Twice I ate a seafood ensemble that was baked and served in a clay-pot. Fantastic! So if you see anything in a clay-pot on the menu, order it.
Lastly, what sort of restaurant is this. It's where you ask your girlfriend for her hand in marriage. It's where you take your wife for your 10th wedding anniversary. It's where you take your Mom or Dad for their 75th birthday celebration. Expect it to hurt your wallet (or better yet, your company's expense account), but you'll enjoy the experience.