Don't scare the fish

Today was my brothers birthday dinner, and we went to sushi. On the glass where the fish was kept a sign was posted don't tape the glass it will scare the fish. With the fish being already dead I thought it was pretty clever.
https://www.google.com/search?biw=1564&bih=720&tbm=isch&sa=1&ei=Ubw_Xfj7B_Gs0PEPn5GFqAI&q=dont+knock+on+the+glass+&oq=dont+knock+on+the+glass+&gs_l=img.3..35i39.3612