Freshwater

Estuaries are more than just the mudflats that we cross on the way to the beach. Of course they have intrinsic value – what natural environment doesn’t? – but they also provide us humans with a range of ecological services that help to sustain the quality of our environment, and with amenities that we all enjoy, and sometimes profit from.

Over the past decade, NIWA has published many popular articles that deal with estuaries - this overview is intended to bring together and make whole sense of the information published to date in the various popular articles.

An estuary is a semi-enclosed embayment, with a free connection to the sea at one end and a freshwater supply at the other, and within which fresh and salty waters mix.

Salmon, Trout and Char (Salmonidae) The Salmonidae family is native to the Northern Hemisphere, but several species have been introduced to New Zealand. Some of these species, particularly brown and rainbow trout, have established very successfully here and support New Zealand’s reputation as an angling Eldorado.

Other live bearers (Phallocerus caudimaculatus, Poecilia latipinna, P. reticulata, Xiphophorus helleri) In addition to mosquitofish, there are four other species of Poeciliidae in New Zealand. As all of these have a very restricted distribution, they have been combined for this discussion. They are all popular aquarium species (who has not heard of the guppy) and probably came to be released by aquarists either tired of looking after their fish or eager to establish feral populations in New Zealand.

LIVE BEARERS (Poeciliidae) As the common name of this family implies, the Poeciliidae are characterised by giving birth to live young. Other family characteristics include a single soft-rayed dorsal fin and no lateral line. On male poeciliids, the anal fin has evolved into a structure known as a gonopodium that is used to transfer sperm bundles to the female fish.

Mackinaw (Salvelinus namaycush)
This member of the Salmonidae family occurs naturally throughout the north of the United States and in Canada and Alaska. A single importation of eggs occurred in 1906, and these fish were destined for Lake Kaniere on the west coast. However, when their transport ran into difficulties crossing Arthurs Pass, the fish were dumped into Lakes Grasmere and Pearson in the Waimakariri River catchment.

Whitebait and mudfish (Galaxiidae) The Galaxiidae family is the largest family of freshwater fishes in New Zealand; there are about 26 species present here which have been divided into two genera, the galaxiids (Galaxias spp.) and the mudfish (Neochanna spp.). Galaxiidae occur throughout the southern hemisphere - in New Zealand, Australia, South Africa, Chile, and Argentina. The family contains some species that are widespread and familiar to most New Zealanders, e.g. the 5 whitebait species, but other species are less well known with very restricted distributions, e.g.

Bullies (Eleotridae)
Redfin Bully
Members of the bully family occupy marine and fresh waters in the tropical Pacific and southeast Asia. There is just one freshwater genera in New Zealand, Gobiomorphus, with seven species: Gobiomorphus alpinus (Tarndale bully) Gobiomorphus basalis (Crans bully) Gobiomorphus breviceps (upland bully) Gobiomorphus cotidianus (common bully) Gobiomorphus gobioides (giant bully) Gobiomorphus hubbsi (bluegill bully) Gobiomorphus huttoni (redfin bully) Bullies have rounded tails, two dorsal fins, a blunt head, and are quite stocky.

CARPS (Cyprinidae) The Cyprinidae family is one of the largest of the freshwater fish families with about 1450 known species. None are native to New Zealand, but several species have been introduced here. Generally carp have large scales, small barbels around their mouth, and no adipose fin. There are many exceptions to this, however, as might be expected in such a large family.

FRESHWATER EELS (Anguillidae) Freshwater eels occur in Europe, on the east coast of North America, and throughout the eastern Pacific and Indian Oceans. There are about 16 species in total. Most New Zealanders are familiar with this fish and know what eels look like. However, not everyone is aware that there are two distinct Anguillidae species native to this country, the longfin eel and the shortfin eel. A third eel species, the Australian longfin eel, has recently been discovered in the Waikato River, and may have colonised other river systems in New Zealand.

To find out more about the New Zealand freshwater fishes, the Atlas of NZ Freshwater Fishes provides an overview of the freshwater fish found in New Zealand, fact sheets for each species and links to other resources.