If I channel to make an artificial underground canal or pool, fed by a natural river (and disappearing at the edge of the map), is there a chance small fish (as I understand it, vermin) will populate the canal so that I can fish from it?
What if I let the water run through floor grates or wall grates to keep out crocodiles? As I understand it, this will definitely keep out large fish (creatures, as opposed to vermin) like carps. But what about small fish? I.e. do vermin pass through the floor grates? Or, on the other hand is it possible that the small fish will spontaneously spawn in my artificial pool/canal?
Of course I could build a walled off area with floorgrates over the river, this would let my fisherman fish safely as well. but it's less beautiful and I thought the grate over the river would be more vulnerable to building destroyers.