Featherbacks have slender, elongated, bodies, giving them a knife-like appearance. The
caudal fin is small and fused with the
anal fin, which runs most of the length of the body. Where present, the
dorsal fin is small and narrow, giving rise to the common name of "featherback". The fish swims by holding its body rigid and rippling the anal fin to propel itself forward or backwards. Notopterids have specialized swim bladders. The organ extends throughout the body and even into the fins in some cases. Although the swim bladder is not highly vascularised, it can absorb oxygen from air and also functions to produce sound by squeezing air through a narrow passage into the
pharynx. At least some species prepare nests and guard the eggs until they hatch. ==Species==