to the sea. This perhaps explains why some very big eels have been caught in Mauritius, notably at La Ferme reservoir. In Rodrigues an eel more than 2 metres long was caught in a spring, in the heart of a forest, at Cascade-Pigeon. It is believed that the eel was 100 years old. There is a theory that eels play an important role in ecosystems; they prevent springs from drying up. All three Mauritian species take a silvery colour when they go back to the sea. Shrimps are common on the banks of most rivers. There are about six varieties of shrimps, and some of them are endemic. One type of shrimp is the chevrette grand bras. This shrimp has a transparent body speckled with tiny reddish-brown or black spots. The female, smaller than the male, has two pincers of equal length but of a thinner size. Another type is the crevette chevaquine. It prefers to live near estuaries. Crayfish are also found in many rivers, especially those that are swift running and well oxygenated. A crayfish, locally known as the bétangue, is endemic to Mauritius. It is easily recognized by its pincers, one being much bigger than the other. It is of a brownish-orange colour and can reach a size of . It has nocturnal habits and is becoming very rare. Another variety is the chevrette sonz. It is of a smaller size and has thin pincers. A third variety is the camaron. It is light blue and the male is longer than the female, although the latter is of a bigger girth. Its size can sometimes exceed (pincers included). After hatching, the larvae of most crayfish go to live in the sea, and swim back to the river when they reach adult stage. This migration is often done against fast moving currents, and crayfish have been observed to climb waterfalls by clinging on rocks. Freshwater crabs are often found in waterways close to the sea. During the reproductive period, the adults gather on some riverbanks near the coast. The eggs are swept into the sea by water currents, and on hatching the young are carried into the river or coastal pond by the tides. The crabs feed mostly on algae and other vegetable matter. Soft shell terrapins with long necks have been noticed in some rivers. They are of Chinese origin and were apparently introduced in a river