biology zoology blog benno meyer rochow fish desert water


That sounds suspiciously fishy, doesn’t it

Several early explorers of the Australian interior (and sadly in recent years some tourists as well) have lost their lives there, because they were unable to satisfy their need of fluid intake and died of thirst and dehydration. The Australian desert is dry, hot, and treeless and yet reports from as far ago as 1845 by Eyre and 1861 by Burke and Willis state that Central Australian Aborigines caught fishes and had names for them – in the desert! So, what kinds of fish could possibly survive in the desert? Well, along tropical seashores one can meet the so-called mud skippers, a group of fishes that hop along tidal flats, the sandy beach or may even climb onto the lower branches of mangrove trees in search of food, like insects, spiders, and worms perhaps that they consume on land. Eels, too, are known to be able to survive out on land especially when in wet grass for some days. Even some catfish have been reported to survive for a while out of water. However, none of that applies to the Australian desert species.

Fact is that even in central Australia there are some deep waterholes, some artesian springs and most of all ephemeral rivers and creeks which after the occasional and sporadic rains can link scattered waterholes and allow some species to exploit the short existence of lakes and rivers. At least 30 species representing 13 families have been described from the central Australian drainage system. Best represented amongst these desert fishes are the Plotosidae (eel-tailed catfishes), Atheriidae, (hardyheads also termed silversides) and Teraponidae (terapon perches, also called grunters). Most widely dispersed are the Lake Eyre hardyhead (that tolerates a range of 0 to 11% salt content in the water: Glover & Sim 1978), bony bream, spangled perch, desert goby and central Australian catfish.

What these species have in common physiologically is that they are tough. They need to tolerate large temperature fluctuations, salinity variations and low dissolved oxygen levels in the water. One of the toughest in these regards must be the desert goby Chlamydogobius eremius. That little fish of finger length tolerates periods of up to 27 days in distilled water and 60 days in water of 3.7% salinity (about that of Mediterranean seawater). It survives temperature extremes of 5°C and 40°C and inhabits waters in which the oxygen concentration can drop to 0.8 mg O2/litre. Of course this and other Australian desert fish must be able to reproduce rapidly and make use of sudden and unexpected, but only briefly lasting enlargements of their aquatic habitats. The Australian species assemblage, however, does not contain killifish, the true champions amongst the fishes of dry habitats.

Killifish (Cyprinodontidae) have many enthusiasts amongst Aquarians, last but not least because they are small, colourful, and easy to keep and because of their unique mode of reproduction amongst fishes. Killifish prefer puddles as a habitat and are known to often leave the puddle and hunt for food on land. They occur across Africa and South America and have some of the shortest life cycles of all vertebrates. The African turquoise killifish Nothobranchius furzeri completes its life cycle in about 10 weeks. During that time it grows from an egg to an adult; it mates, lays its eggs into the soil and dies. The eggs are so resistant to drying out, that they can be sent in an envelope to other killifish enthusiasts. The development stalls and the eggs enters a dormant stage as long as there is no water. The dormancy can last for weeks. Although there are generally male and female individuals and true copulations occur (rare in fish other than live-bearers like guppies, swordtails and platy fish) there is one extraordinary species that can fertilise itself: the American mangrove killifish (Kryptolebias marmoratus). It has one other record to its credit: it has been reported to be able to survive without water for 66 days! Compared with a human that under the best circumstances won’t last longer than a few days, I’d say that’s quite a feat.

© Dr V.B. Meyer-Rochow and, 2020.
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