parky i am not sure if agios nikolaos has beaches for snorkelling in order to see fishes, as the majority of them have sand. Still though going to the far sides for the beaches normally you will find rocks, thus fishes. been ages since the last time i went for a swim in Agios nikolaos so i cant recoment a particular one. The only one that comes in my mind is Kitroplatia.
Jathson visiting malia for a night not only help you realise how good stalis is, but will also help you realise how bad the youths can be when in holidays....