but then no animal migrates or no reason, and usually its for food, so if food is provided year round, there will be no reason for migration. and they will happily not make that trip.
water temps I wouldn't know anything about...
and why do they dive? is that for food? or are there other reasons?
and I don't understand the difference here, why is it one rule for small fish that we can keep at home and a completely different rule for fish that are too big for our home aquariums? like cardinal tetras are very active fish (usually) and yet we would happily say that a tank 20 inches long is more than long enough for them...