Otters are carnivorous mammals in the subfamily Lutrinae .The 13 extant otter species are all semiaquatic , aquatic or marine , with diets based on fish and invertebrates . Otters have long, slim bodies and relatively short limbs . The 13 species range in adult size from 0.6 to 1.8 m (2.0 to 5.9 ft) in length and 1 to 45 kg (2.2 to 99.2 lb) in weight. Males weigh up to 90 lbs (41 kilograms).The Oriental small-clawed otter is the smallest otter species, which grows up to 2.9 feet (90 centimeters) long and up to 11 lbs. (5 kg) and the giant otter and sea otter are the largest. They have very soft, insulated underfur, which is protected by an outer layer of long guard hairs . This traps a layer of air which keeps them dry, and warm. For most otters, fish is the staple of their diet. This is often supplemented by frogs, ...