Macroecological patterns in the New Zealand freshwater fish fauna are structured largely around the presence and absence of diadromy. All diadromous species are present across nearly the entire latitudinal range of New Zealand, and they exhibit general sympatry with other diadromous species, whereas non-diadromous species have much narrower latitudinal ranges, the species composition of communities changes progressively from northern to southern latitudes, and there is widespread allopatry. Inland penetration of diadromous species varies widely with some restricted to lowland habitats close to the sea, whereas other species penetrate varying distances inland. As a result there is downstream-upstream decline in species richness of diadromous fish communities, as one species after another drops out of the communities, with increasing distance inland/elevation, a form of nestedness. Species richness at any latitude is dominated by diadromous species. Non-diadromous species vary widely in their centres of occupation, though many of them are most commonly found at sites well upstream from the sea. Non-diadromous species are largely absent from small islands around New Zealand, probably because island streams are small and ephemeral.