Australasia (Australia, New Zealand and New Guinea) contrast markedly in size, climate and the diversity of freshwater fishes. Although Australia is the largest landmass, it has a smaller native fish community (256 species) than Papua New Guinea (PNG) (340 species), while New Zealand has 38 species. Aquaculture in all three countries is mainly based on introduced species (Atlantic salmon Salmo salar in Australia, Chinook salmon Oncorhynchus tshawytscha in New Zealand and tilapia Oreochromis spp. and common carp Cyprinus carpio in PNG). While there are small, modest commercial fisheries for native species in all countries, there are also important customary fisheries by indigenous people.
Australia supports significant freshwater fisheries resources, comprising both finfish and invertebrate species. Fisheries have long played key cultural and dietary roles for Aboriginal communities. Fisheries differ across the country, with endemic, high‐value finfish in the south‐east's Murray–Darling Basin (MDB). In the north and north‐east, commercial fisheries exploit silver barramundi Lates calcarifer. Eels are also harvested from south‐eastern coastal rivers.
Recreational fishing has progressively displaced commercial harvesting of finfish around the country, particularly in the east. Widespread river impoundment created expansive artificial habitats that are routinely stocked with fish propagated for angling, and favoured species are often protected from marketing. Aquaculture production is focused on a few high‐value table species, together with native and salmonid angling species destined for stocking in recreational fisheries, and conservation programmes for threatened species.
Alien species contribute to production; five salmonids support recreational and commercial fisheries, while C. carpio and perch Perca fluviatilis are also exploited in some areas. Alien fishes generate substantial ecological changes in Australian fresh waters. Extensive declines have been documented among most freshwater resources, particularly in the MDB, where finfish populations have fallen to c. 10% of pre‐European levels. Many species are threatened. Catchment and habitat changes following agricultural development, species invasions, overexploitation and obstruction of migration pathways by innumerable dams and weirs have all been implicated.
In contrast to Australia where extensive areas are arid or semi‐arid, New Zealand has generally abundant rainfall, but steep topography results in rapid runoff. Half the native fish fauna are diadromous, maintaining some connection with the sea. Two thirds of native species are threatened in some way, and one species is extinct. The customary (Maori) fishery is largely focused on freshwater eels, and there are areas set aside for exclusive customary fishing. Likewise, commercial fishing is focused on eels (c. 500 t year−1); although smaller catches of mullet (mugilids) and flounders Rhombosolea spp. are made, all these species are managed within the Quota Management System whereby fishers are allocated annual catch entitlements. The main recreational fishery for native fishes is for juvenile galaxiids (whitebait) at river mouths in spring. New Zealand, however, is renowned for its wild trout fishing (usually brown trout Salmo trutta in rivers and rainbow trout Oncorhynchus mykiss in lakes). Farming of trout is not allowed in New Zealand, but there is a growing farming industry for O. tshawytscha, mainly in sea pens but also in large nets in hydro canals.
Many rivers have minimum flows and maximum abstractions set to protect environmental, recreational and cultural values. Substantial increases in dairying over the past two decades have resulted in increasing demands for water, often resulting in increased nutrient loads to surface and groundwaters. Predicted effects of climate change are to exacerbate existing conditions with presently wet areas becoming wetter and dry areas drier. Native fishes will show more resilience to such changes than introduced species.
PNG has a wet tropical climate, and rainfall is not strongly seasonal. The lowland reaches of rivers are low gradient and turbid and support a high diversity of fish species, many of which are migratory within fresh water or require access to the sea. PNG is the largest producer of freshwater fishes in Australasia, with an estimated production of 17,500 t year−1. Lates calcarifer are the most economically important species; the fishery collapsed in the 1990s due to the combined effects of mining and overfishing but is now recovering. River herring Nematalosa papuensis, several catfish species and tropical snappers are also important harvested species. Fishing is mainly a subsistence activity carried out by women and children, and freshwater fishes are the main source of protein to people in inland areas. Of the 25 introduced fishes, three tilapia species and C. carpio provide the basis for extensive but small‐scale aquaculture. There is growing concern about the impacts of introduced species on the native fish biodiversity, while poorly managed mining, forestry and agriculture have led to declining fish stocks in some rivers. Management strategies need to involve increased engagement of these industries while supporting the use of traditional customs to manage local fisheries.