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Former mariners in New Guinea’s rivers and lakes
The ancestors of New Guinea’s fish once swam in the warm waters of the Indo-Pacific Ocean. Now they follow the currents of the island’s freshwater bodies, marvellously adapted to life in radically different conditions.

Most fishes found in freshwater are either migratory, coming from or going to the sea to spawn - such as the tarpon (Megalops cyprinoides), barramundi (Lates calcarifer) - or are permanent inhabitants of freshwater habitats. In the second category, these fish belong to or are derived from marine families. Examples include fork-tailed catfishes (family Ariidae), gudgeons (family Cyprinidae), gobies (family Gobiidae), grunters (family Terapontidae) and jacks (family Carangidae).

The only fish considered not to have derived from marine ancestors is the bony tongue (Osteoglossiformes).1

A fish map of New Guinea

Freshwater fishes living in the south of the island are generally different species to those in the north, unless they are capable of migrating through the sea. In general, southern rivers have a much higher diversity of fish species than northern rivers. 2

Where the fish live:3

  • Blackwater streams
    Catfishes (order Siluriformes), rainbowfishes (family Melanotaeniidae),  gudgeons (family Cyprinidae) and gobies (family Gobiidae) are found here. These rivers are generally richer in fish fauna than the large, muddy rivers, and there are many fishing villages next to them.
  • Lowland rivers
    Turbid waters and silty or muddy bottoms make for poor aquatic vegetation and hence less fish life. Here we can find catfishes, which are common, along with marine visitors such as croakers (family Sciaenidae), silver biddies (family Gerreidae), ponyfishes (family  Leiognathidae) and juvenile trevally (Caranx species).
  • Floodplain lakes, swamps and backwaters
    Cover huge areas with good quality water, rich in aquatic plants providing ample hiding places for juvenile fish. Common here are rainbow fishes, gobies, gudgeons and the ubiquitous catfishes.
  • Upland tributaries
    Very clear water, rapidly changing level and a general lack of aquatic plants. Common here are eel-tailed catfishes, rainbowfishes, hardyheads (Craterocephalus kailolae), grunters, gudgeons (especially the genera Oxyeleotris and Mogurnda) and gobies, many of the genus Glossogobius.

Exclusively freshwater fish

More than 200 fish species in New Guinea have evolved to the point where they are limited to freshwater. About 150 of those are found nowhere else in the world (they are endemic).

For example, rainbow fishes (family Melanotaeniidae) and blue-eyes (family Pseudomugilidae), 2 closely related families, are unique to Australasia - an area that includes Australia, New Zealand, New Guinea and many smaller islands in the vicinity. 4

The fish bounty of the Fly River

The Fly River floodplain abounds with vital nutrients and food supplies. For migratory species such as the barramundi (Lates calcarifer), which feeds largely on herrings (Nematolosa species), such productivity is critical for survival. For other fish, important food items include invertebrates, algae, plants and organic detritus.

The fish species of the Fly River have evolved astute strategies to survive the severe droughts that can afflict the region: Few of them bother to specialize on a single food or habitat type. As a result, most resident species are widely distributed.

There are very good reasons why a fish would choose this strategy. A close overlap in diet and habitat requirements allows a species to survive in times of hardship – when the water flow and level falls or when some food items are scarce.5

A closer look at…

1 Coates, D. 1989. Review of Aquaculture and Freshwater Fisheries in Papua New Guinea - A report prepared for project PNG/85/001 Sepik River Fish Stock Enhancement Project. FAO. Field Document No. 1. PNG/85/001.
2 Coates, D. 1989. Review of Aquaculture and Freshwater Fisheries in Papua New Guinea - A report prepared for project PNG/85/001 Sepik River Fish Stock Enhancement Project. FAO. Field Document No. 1. PNG/85/001.
3 Muller, based on Allen.
4 Miller S. (Ed). 1994. Status of biodiversity in Papua New Guinea: Papua New Guinea Country Report on Biological Diversity. Waigani: The Department of Environment and Conservation, Conservation Resource Centre and the Africa Centre for Resources and Environment (ACRE); 67-95.
5 Swales, S. Undated. FISH AND FISHERIES OF THE FLY RIVER, PAPUA NEW GUINEA: Population Changes Associated with Natural and Anthropogenic Factors and Lessons to be Learned. World Fisheries Trust / IDRC /UNEP. 26 pp.