though japanese does not tend to stress syllables and has a very constant beat to it compared to english etc., you see some minor variance in stressing like a short う sound (or す rather) e.g. sometimes at the end of words e.g. です and います. When people stress です into 2 syllables, thinking they must pronounce the "u" in "desu" it sounds pretty cringe so I guess you've just got to learn the exceptions.
The fish does need to be fresh. However, the best sushi chefs, freeze their fish after purchase to allow the flavor to develop. It's usually frozen for 24-48 hours. Also the most important taste of the sushi is in the rice. Choosing the right rice, and cooking it correctly can make or break sushi.