The catfishes in the Neotropical subfamily Vandelliinae (family Trichomycteridae) feed exclusively on blood as adults, a very rare feeding specialization among vertebrates (the lampreys and vampire bats being the obvious examples). Their hosts are larger fishes.
Little is known about vandelliines. The recently discovered juveniles are apparently predators on small aquatic invetebrates, as is the case for most other trichomycterids from other subfamilies. The structure of the mouth of juvenile vandelliines also resembles that of non-parasitic trichomycterids, but juvenile vandelliines undergo a metamorphosis during which their mouth structure transforms to the highly modified adult blood-feeding morphology.
(De Pinna 2006)