Largetooth sawfish
Adults are primarily found in estuaries and marine waters to a depth of , but mostly less than . Nevertheless, the species does appear to have a greater affinity for freshwater habitats than the smalltooth sawfish ("P. pectinata"), green sawfish ("P. zijsron"), and dwarf sawfish ("P. clavata"). Largetooth sawfish from the population in Lake Nicaragua appear to spend most, if not all, of their life in freshwater, but tagging surveys indicate that at least some do move between this lake and the sea. Captive studies show that this euryhaline species can thrive long-term in both salt and freshwater, regardless of its age, and that an acclimation from salt to freshwater is faster than the opposite. In captivity they are known to be agile (even swimming backwards), have an unusual ability to "climb" with the use of the pectoral fins and they can jump far out of the water; a individual jumped to a height of . It has been suggested that this may be adaptions for traversing medium-sized waterfalls and rapids when moving upriver. They are generally found in areas with a bottom consisting of sand, mud or silt. The preferred water temperature is between , and or colder is lethal.
Snailfish
In October 2008, a UK-Japan team discovered a shoal of "Pseudoliparis amblystomopsis" snailfish at a depth of approximately in the Japan Trench. These were, at the time, the deepest living fish ever recorded on film. The record was surpassed by a snailfish that was filmed at a depth of in December 2014 in the Mariana Trench, and extended in May 2017 when another was filmed at a depth of in the Mariana Trench. The species in these deepest records remain undescribed, but it has been referred to as the "ethereal snailfish". The deepest-living described species is "Pseudoliparis swirei", also of the Mariana Trench, which has been recorded to . In general, snailfish (notably genera "Notoliparis" and "Pseudoliparis") are the most common and dominant fish family in the hadal zone. There are indications that the larvae of at least some hadal snailfish species spend time in open water at relatively shallow depths, less than .