The Brook of Ripa Sottile (1941)

Upstream river Ripasottile a shoal of perch fish have born. The news spreads around all animals who live around the river, until also the trouts hear about it, and swim upriver to go eat the newborn fish. So all animals around the river and from the wood organize a desperate expedition to fight the trouts back. At the end the birds manage to wake a fisherman up, just in time to have him catch all the trouts with a single haul.