Eels · waters

The waters behind the fish

The “eels” are creatures of very different waters — an alkaline rift lake in Tanzania, a rice paddy in the Mekong delta, a blackwater peat swamp in Borneo, a Yucatán cenote, a cold European river that a true eel will leave to cross an ocean. Knowing which system a species comes from — its temperature, chemistry and flow — is the foundation of keeping it well, and explains why a Tanganyikan rift eel and an Amazonian swamp eel want such different tanks. Here are the freshwater systems that shaped 128 of the 133 species in this atlas.

The African Great Lakes & rift

14 species

East Africa · Lake Tanganyika & the rift valley

The deep rift lakes of East Africa — above all Lake Tanganyika, where the spiny eels did what the cichlids did and exploded into a species flock found nowhere else. A dozen-plus rock-dwelling Mastacembelus, several restricted to single stretches of shoreline, share these clear, alkaline, oxygen-rich waters with the lake's famous cichlids. A textbook case of lacustrine radiation in a fish family better known from rivers.

West & Central African rivers

36 species

West & Lower Guinea · the Niger, Congo & Volta

The forest rivers and savanna floodplains of West and Central Africa — the Niger, Congo, Volta, Cross and the coastal drainages from Guinea to Angola. Home to a wide range of river-dwelling Mastacembelus and the African swamp eel (Ophisternon), alongside the catadromous African mottled eel (Anguilla) that runs up these rivers from the Atlantic. Soft, warm, often tannin-stained waters.

The Nile, Zambezi & East African coast

4 species

Sudano-Zambezian Africa · the Nile, Zambezi & Indian-Ocean coast

The great north–south river systems of eastern Africa — the Nile and the Zambezi — and the short coastal rivers that drain to the Indian Ocean, including those of Madagascar. The range of widespread river Mastacembelus and the African and giant mottled eels (Anguilla mossambica, A. marmorata, A. bengalensis labiata), true eels that migrate in from the western Indian Ocean to grow in fresh water.

India & the Gangetic plain

23 species

South Asia · India, Sri Lanka, Bangladesh & Nepal

The rivers, tanks, paddies and hill streams of the Indian subcontinent — the Ganges and Brahmaputra plains, the peninsular rivers and the Western Ghats. A spiny-eel stronghold (the zig-zag eel Mastacembelus armatus, the many Macrognathus), the rice-paddy swamp eels (Monopterus, Ophisternon), and the Indian mottled eel (Anguilla bengalensis) that climbs the rivers from the Bay of Bengal.

Mainland Southeast Asia

27 species

Indochina · the Mekong, Chao Phraya, Irrawaddy & Salween

The great floodplain rivers of mainland Southeast Asia — the Mekong, Chao Phraya, Irrawaddy and Salween, with their paddies, swamps and oxbows. The aquarium heartland of the spiny eels: the fire eel (Mastacembelus erythrotaenia), the tire-track eel (M. favus), and the peacock eels (Macrognathus), alongside the abundant Asian swamp eel (Monopterus albus) of every rice field.

Sundaland & the Malay archipelago

6 species

Sundaland · the Malay Peninsula, Sumatra, Borneo & Java

The forest streams, blackwater peat swamps and great rivers of the Malay Peninsula, Sumatra, Borneo and Java. The other home of the fire eel and many Macrognathus, the Sundaic swamp eels, and the Indonesian shortfin eel (Anguilla bicolor) — a tropical true eel that, unusually, spawns in the eastern Indian Ocean rather than across the world.

East Asia — China, Japan & Korea

2 species

Temperate East Asia · the Yangtze, Pearl River & the Japanese archipelago

The rivers, lakes and paddies of China, the Korean peninsula and the Japanese islands. The core range of the Asian swamp eel (Monopterus albus) — a food fish across the region — the Chinese spiny eel (Sinobdella sinensis), and the Japanese eel (Anguilla japonica), the catadromous true eel that fuels the unagi trade and is now Endangered.

The Indo-Pacific & Oceania

9 species

The tropical Pacific · New Guinea, the Pacific islands, Australia & New Zealand

The island and continental fresh waters of the western and central Pacific — New Guinea, the Philippines, the Pacific archipelagos, and the temperate rivers of Australia and New Zealand. Almost entirely a true-eel realm: the giant mottled eel (Anguilla marmorata) and its tropical-Pacific relatives, and the Australasian longfin and shortfin eels (A. reinhardtii, A. australis, A. dieffenbachii), some of which migrate astonishing distances to spawn.

The North Atlantic — Europe & eastern North America

4 species

The Atlantic basin · Europe, North Africa & eastern North America

The rivers, lakes and estuaries draining to the North Atlantic, on both sides of the ocean. The realm of two great catadromous travellers — the European eel (Anguilla anguilla) and the American eel (A. rostrata) — which spawn together in the Sargasso Sea and drift back as glass eels to grow in fresh water. Both are in steep decline: the European eel is Critically Endangered.

Tropical America

3 species

The Neotropics · the Amazon, Orinoco, Paraná & Mesoamerica

The swamps, floodplains and cave systems of tropical America, from Mexico to Argentina. The home of the New-World swamp eels — the wide-ranging marbled swamp eel (Synbranchus marmoratus) of the Amazon, Orinoco and Paraná, and the Ophisternon swamp eels of the Caribbean lowlands and the blind cave eels of the Yucatán. No spiny or true eels here; this is Synbranchidae country.

Other waters

5 species

Worldwide

Eels and their look-alikes whose recorded range falls outside, or spans, the named systems above — including widely-distributed swamp eels and several little-collected African and Asian spiny eels known from a single river. The hydrology of these three families is intricate and incompletely mapped, and the taxonomy of the African spiny eels in particular is still moving.

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