Arowanas & Oddballs · waters

The waters behind the fish

The bonytongues come from wildly different waters — a flooded Amazon várzea where an arowana cruises the surface, a tea-black Congo tributary where an elephantnose reads its world by electric field, a monsoon-swollen Mekong holding a metre-long clown knife, a peat swamp in Borneo that is the last wild home of the Asian arowana. Knowing which system a species comes from — its temperature, hardness, flow and how dark its water is — is the foundation of keeping it well, and explains why an Amazon silver arowana and an African elephantnose want such different tanks. Here are the freshwater systems that shaped 197 of the 201 species in this atlas.

The Amazon & the Guianas

6 species

Tropical South America · the Amazon, Orinoco & the Guiana Shield

The New-World home of the bonytongues. The Amazon and Orinoco basins and the rivers of the Guiana Shield hold the two Osteoglossum arowanas — the silver of the whitewater and floodplain, the black of the Rio Negro's blackwater — and the arapaima (Arapaima), one of the largest freshwater fish on Earth, an air-breather of the várzea floodplain lakes. Warm, soft and often tea-stained water, seasonally flooded forest. The silver arowana is a surface-cruising jumper and a paternal mouthbrooder; the arapaima is the ultimate size trap.

The Congo basin

106 species

Central Africa · the Congo (Zaire) river & its tributaries

The immense rainforest river of Central Africa — the second-largest on Earth by discharge — and a global centre of mormyrid diversity. The Congo and its tributaries (the Kasai, Ubangi, Lualaba) hold dozens of elephantnoses and mormyrids (Campylomormyrus, Marcusenius, Petrocephalus, Stomatorhinus, Mormyrus), the African brown knifefish Xenomystus and the featherback Papyrocranus, the African arowana Heterotis and, in the north, the aba Gymnarchus. Warm, soft, often tannin-stained water — the dark, weakly electric world the mormyrids evolved to read.

West Africa & the Niger

39 species

West Africa · the Niger, Volta, Senegal & the Guinean rivers

The Niger and Benue, the Volta, the Senegal and Gambia, and the short forest rivers of Upper and Lower Guinea — the aquarium heartland of the African bonytongues. Here are the elephantnose Gnathonemus petersii and many other mormyrids (Mormyrus, Marcusenius, Petrocephalus, Brienomyrus, Pollimyrus, Hyperopisus), the African butterflyfish Pantodon buchholzi of the quiet, soft forest pools, the African arowana Heterotis niloticus, the featherback Papyrocranus afer, and the air-breathing electric aba Gymnarchus niloticus. Warm, seasonally flooded, mostly soft water.

The Nile & Lake Chad

12 species

Sudano-Sahelian Africa · the Nile, Lake Chad & the Sahel rivers

The Nile from the Sudd to the delta, the Lake Chad basin and the Sahelian floodplains — the water where Europe first met the mormyrids (the ancient Egyptians carved Mormyrus into tomb reliefs). Home to the aba Gymnarchus niloticus, the African arowana Heterotis niloticus, and a suite of mormyrids (Mormyrus, Hyperopisus, Marcusenius, Petrocephalus, Mormyrops, Hippopotamyrus). Seasonally flooded, warm, often turbid water — several of these are air-breathers that endure the dry season in shrinking pools.

The Zambezi & East Africa

24 species

Southern & Eastern Africa · the Zambezi, the Great Lakes & the coastal rivers

The Zambezi and Okavango, the Kafue and Limpopo, the East African coastal rivers (Rufiji, Rovuma, Tana) and the Rift Valley lakes. A southern mormyrid fauna — Marcusenius, Petrocephalus, Cyphomyrus, Hippopotamyrus, Mormyrus, Mormyrops (the giant bulldog Mormyrops anguilloides reaches 1.5 m) — plus Heterotis where it has been introduced. From clear, seasonal southern rivers to the swamps of the Okavango delta.

The Mekong & mainland SE Asia

6 species

Indochina · the Mekong, Chao Phraya, Irrawaddy & Salween

The great floodplain rivers of mainland Southeast Asia. The Mekong and Chao Phraya are the home of the featherback knifefishes — the clown knife Chitala ornata, the giant Chitala lopis, and the grey featherback Notopterus notopterus — and of the Asian arowana Scleropages formosus in its northern range. Warm, monsoon-driven, seasonally flooded water; the clown knife is a metre-long ambush predator and a classic size trap, farmed for food and for the trade.

Sundaland & the Malay archipelago

2 species

Sundaland · the Malay Peninsula, Sumatra & Borneo

The forest streams, blackwater peat swamps and great rivers of the Malay Peninsula, Sumatra and Borneo (the Kapuas, Batang Hari, Musi, Barito). The stronghold of the Asian arowana Scleropages formosus — the red and gold colour forms are wild races of the peat-swamp and river systems here, and the fish is listed on CITES Appendix I — alongside the featherbacks Chitala and Notopterus. Water ranges from acidic, tea-black peat swamp to clear hill stream.

Australia & New Guinea

2 species

Sahul · the tropical rivers of northern Australia & New Guinea

The fresh waters of northern Australia and New Guinea, home to the two Australasian arowanas — the northern saratoga or gulf saratoga Scleropages jardinii of the Jardine, the Fly and the northern drainages, and the spotted saratoga Scleropages leichardti of the Fitzroy and Dawson in Queensland. Like all arowanas they are surface-cruising jumpers and mouthbrooders. Warm, seasonal tropical rivers, billabongs and clear upland streams.

Other waters

4 species

Worldwide

Bonytongues whose recorded range falls outside, or spans, the named systems above — including introduced or farm-escaped populations and several little-collected African mormyrids known from a single river. Osteoglossiformes is incompletely mapped and its taxonomy is still moving, so some species sit here until their range is pinned down.

← Browse the species index