THE NOTHOBRANCHIUS SITE

Fish fall from the Sky with the Rain…

 

     The amazingly colourful Nothobranchius fishes occur mainly in eastern and south-eastern Africa. They are recognized as annuals, since their life-cycle is geared to the periodic drying up of their natural habitats, typically seasonal pools, rivers and swamps. This periodicity is determined by the rainfall pattern of the regions in which the habitats occur. Before the temporary waters dry out completely, spawning takes place and the eggs survive the dry season buried in the mud. When the rainy season arrives, the rivers overflow their banks and inundate the floodplains, the buried eggs hatch and the amazing cycle of life is started again, providing a reminder for us of how wonderfully organized nature is.

 

     One of the intense pleasures of traveling in Africa is the opportunity to live among people who have not forgotten the myths of the elders. People of the Luba communities, living in Katanga province of Democratic Republic of Congo, told me a legend that fish fall from the sky with the rain. And it indeed happens like that...! If a hollow is made in the terrain somewhere in the vicinity of a river, one month after the rains arrive, when the locality has been filled with water, small fish could be found in there.

 

     On another account, back in 1837 when Ignatius Pallme undertook a voyage in Sudan, research into the reproductive biology of the different fishes was still in its infancy. Pallme visited the Kordofan region, which lacked permanent flowing waters, and all the ponds and small lakes dried out during the dry season. Yet fish, he said, differing in variety and size, were found in this province. At first he did not understand this seeming anomaly, as the explanation given by the native people, that the fish hide in the mud, appeared to him unsatisfactory because the substratum “becomes in time, so hard that a heavily laden waggon might pass over it, and the spawn of the fish remaining would, of course, be soon destroyed by the rays of the sun.” The natives, however, firmly believed the fish are preserved underground, and come to life again in six months' time, when the rain has softened their bed. Pallme stated that he, of course, could not give credence to the story, but casually reported a discovery likely to throw some light on the subject. One day he shot a wild duck and proceeded to prepare it for dinner; in examining the intestinal tract, he found a quantity of fish eggs. Therefore, he speculated that birds might discharge one part of their prey in an undigested form, and thus the fish would be shortly hatched.

 

     This kind of stories nicely illustrates the ancient relation of people to nature in Africa. Today, we know much more about the reproductive biology of different fishes, recognizing that certain species have adapted to ensure their survival of the harsh conditions during the dry season.

 

     The region around the Rift Valley in Eastern Africa is well known as the home of the earliest human ancestors, so it might also have been the home to the first fishermen on Earth. I have visited eastern and south-eastern Africa on several occasions and I was always fascinated by the fabulous natural features of the region. In this part of the world, everything feels stronger, the sunshine is hotter and even the colours are more vibrant. That, and the excitement of discovery when collecting killifishes there, are the reasons I return again and again...

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