Abstract
This review examines possible estuarine fish colonisation processes of the Pacific Ocean that started in the Early Jurassic and gained momentum with the break-up of Pangea. Initial colonisation of the newly-created estuaries by fish is likely to have accelerated during the Devonian, with tropical marine families from the Neotethys Sea region using epicontinental seaways between Asia, Australia, India, Arabia, Europe and the Americas to colonise estuaries on these drifting land masses. Analyses of the presence/absence of fish families and species from selected ecoregions around the Pacific Ocean rim showed that estuary-associated fish families on the eastern and western side of the Pacific Ocean separated out at a Bray-Curtis similarity of 41 % but were only ∼5 % similar at the species level. In terms of past and present geodispersal of fish taxa, tropical species may have used ‘island hopping’ to cover the >19 000 km gap between the tropical western and eastern shores of the Pacific. However, most tropical taxa in the eastern Pacific appear to have originated from the Caribbean area of the Western Atlantic and not from the central Western Pacific fish species ‘hotspot’. In contrast, ichthyofaunal colonisation of Western Pacific regions to the north and south of the ‘hotspot’ was facilitated by ocean currents and the more limited distances between estuaries and coastal ecoregions in this part of the Pacific. The cold temperate waters of the Northern and Southern Pacific Ocean would have acted as a barrier to tropical species attempting to use these routes to cross the Pacific Ocean basin. The prevalence of temperate diadromous fish species in both the temperate northern (e.g. Russia and Alaska) and southern (e.g. New Zealand and Patagonia) estuaries is probably a function of local evolutionary trends that favoured such taxa in those particular regions.