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Author: Rudy van der Elst
These natural history guides have been developed in the hope that young people and anyone with a budding interest in natural history will take up the challenge to learn the secrets of southern Africa’s fascinating fauna and flora.
These little guides are an invaluable resource for the beginner, providing information at a glance through superb photographs, maps and easy-to-read text.
• handy pocket size
Professor Rudy van der Elst is director of the Oceanographic Research Institute (ORI) based at Durbans uShaka Marine Park. He works with a team of scientists in focusing in particular on sustainable harvesting of resources and the protection of marine biodiversity. Rudy has published many scientific and popular articles and books on marine topics.
Fish are fascinating creatures. They are the most numerous back-boned animals (vertebrates) on earth, and display an amazing variety of adaptations and unique biological features.
Since their first appearance on earth almost 400 million years ago, fish have evolved and dispersed to colonise virtually every body of water on earth. They range from the deepest of oceans to the highest mountain streams and from freezing polar seas to tropical lagoons and hot springs.
The southern African region is endowed with 160 species of freshwater fish and more than 2 200 species of sea fish, which is about 15 % of the worlds total. This variety is due in part to the many different habitat types found on the southern African coastline.
Most common of all fishes are the bony fish, which have skeletons made entirely of bone and also an airbladder (to control their buoyancy), scales which cover the body, and a single gill opening on either side of the head. Included in this group are marine and freshwater types, ranging from minute gobies to giant and powerful marlins.
In contrast there are fish which have their skeleton constructed entirely of cartilage. These are the sharks, rays and skates, which all have more than one gill opening on either side of the head and rather fine but sharp scales, known as denticles.
Very few of these occur in freshwater. The world’s largest fish, the harmless Whale Shark, belongs to this group, as do the fearsome Great White Shark and the Manta Ray. Despite their often bad publicity, most sharks are harmless and play an important role in many ecosystems.
Fish are well equipped to survive the often harsh conditions of their natural environment. They are able to breathe, move, forage for food, detect prey and predators, and to navigate in their underwater habitat. This ability to survive and even thrive in this realm allows them to build up the reserves needed to reproduce their own kind.
Estuaries, bays and beaches