fishing is not gerund--since it is limited to "today"

My understanding is that a gerund is a word that has the quality of a verbal noun. In other words, it is a name for describing the state of doing something. So I would have figured:
A fish = noun (name of an object/animal)
To fish = verb (formed from the elided concept of ‘catching a fish’)
Fishing = gerund (the continuing action of the verb-from-the-noun)

That would have led me to find no difference between your two examples of ‘fishing’ – but I think it does still get something of your idea of an ongoing action, doesn’t it?

(and BTW good for you with your outlook on teaching yourself – that’s just what I’m doing here!)

And belM, yes, though my initial way of trying to get at this way in which we stretch one form of word into another form was convoluted, I do think bat and batting is just the same. You could trace the same effect anytime a verb has been formed from the name of an object: say, root - rooting, shoe - shoeing, ball -