Sawfish
Sawfish are primarily found in coastal marine and estuarine brackish waters, but they are euryhaline (can adapt to various salinities) and also found in freshwater. The largetooth sawfish, alternatively called the freshwater sawfish, has the greatest affinity for freshwater. For example, it has been reported as far as up the Amazon River and in Lake Nicaragua, and its young spend the first years of their life in freshwater. In contrast, the smalltooth, green and dwarf sawfish typically avoid pure freshwater, but may occasionally move far up rivers, especially during periods when there is an increased salinity. There are reports of narrow sawfish seen far upriver, but these need confirmation and may involve misidentifications of other species of sawfish.
Smalltooth sawfish
The many teeth of a sawfish's saw are not actually teeth at all, but rather special types of scales known a dermal denticles. These protruding weapons, combined with the animal's ability to strike from side to side with great force, provide it with a powerful and efficient defense mechanism. Although the saw is mainly used for feeding purposes, observations of sawfish in captivity show that they may also be used for self-defense. When sharks or other marine creatures threaten them, they retaliate with three swift blows to the instigator's dorsum. Sawfish are not considered harmful to humans unless they are threatened.