You have to hit A when it says that you have a bite. If you're too slow, it gets away, but the only way that would happen is if you weren't paying attention or didn't know.
I know it, but the game gives you an absurdly short time to hit A after the "Oh! A bite!". You need to either have an impossibly perfect timing or get VERY lucky. And still having the "Not even a nibble..." makes it more frustrating. I never felt so frustrated since i used to try getting right the button sequence to do a Fatality within the time limit in Mortal Kombat.