Loaches belong to the super-order Ostariophysi, sub-order Cyprinoidei, and are grouped under the family Gobitidae. They’ve a lot in typical with the carps, but differ in having 3 or much more pairs of barbels, and they never have teeth in the jaw.
Loaches can survive in damp mud, and damp pockets of dried up pools, by using their intestines for the respiratory function instead of their gills. They’re exclusively all Old World species.