Large species of mammals are more vulnerable in case of the changes taking place in the ecosystem. As a result of ecological accident at the border of Holocene and Neocene efficiency of many ecosystems had fallen also the majority of large predatory mammals had died out. Extinction had affected also some water animals, in particular otters - they had disappeared forever, when many large species of fishes have died out. Later when the situation had stabilized, the place of otters insectivores have occupied - fishing shrew is one of them. The fishing shrew is the descendant of one of species of the Asiatic water shrews (Chimarrogale), dwelt in Holocene at banks of mountain streams in the Central Asia. Length of the body at this mammal is about 40 cm; tail is up to 50 cm. The shape of this animal shows to observer the good swimmer: flat head, long brawny trunk, flattened tail, hinder legs with membranes between fingers. Ears are very short, eyes are shifted to the forward third of head. Brain cavity is low and long, brain is small. The nose of this animal extends to short mobile proboscis. Teeth are sharp, at molars there are 2 - 3 sharp tops, canines are large, slightly jutting out from the closed mouth. The body and tail of the animal is covered with rich fur; fat glands are advanced for greasing hair. Coloring of fur is ochre - red, on the head, tail and paws it is darker, on throat and chest there is white irregular-shaped spot. The mammal spends a lot of time, clearing and greasing fur. Except for fat glands, at an animal also large anal glands are advanced, producing unpleasantly smelling musk secret for protection. On forepaws the thumb has the special "toilet" claw for combing out dust from fur. The fisher shrew eats fishes and small water vertebrates, large water insects (beetles, larvae of dragonflies). It is solitary animal, only the female and its cubs (up to 5 cubs in one pack) live together. Seasonal prevalence in breeding is not present. For cub rearing the female digs in river bank the burrow with exits at the surface and under water. The young growth spends the first 3 weeks of life in burrow, then starts to get out from home and study to swim. Two-month old cubs leave the home for few days, and at the age of three months they live independently. At the age of half-year young animals are already capable to breeding. Life expectancy is up to 6 - 7 years.
In South America the ecological niche of aquatic fish-eater had been occupied by otterodent, the descendant of piscivorous rodent Ichthyomys.