The deep-bodied pipefish (Leptonotus blainvilleanus) is a species of marine fish belonging to the family Syngnathidae. They can be found in shallow estuaries and algal beds along the coast of South America from Ecuador to Argentina. Predators of this species include mackerel and the La Plata dolphin. Reproduction occurs through ovoviviparity: the eggs are carried in a pouch under the tail of the male until they hatch.
This species reaches a length of .
The fish is named in honor of zoologist-anatomist Henri Marie Ducrotay de Blainville (1777-1850)