Mechanism

Mechanism of Hitch-Hiking
Looking at the morphology of Vandellinae we see tendencies to have long snouts, and long and sturdy teeth. Vandellia found on the base of a giant catfish (Zungaro zungaro) had bitten into the host's skin and buried their snouts to the base of the eye. This is probably done in order to enable the Vandellia to continuously monitor the environment so as to know when to release from the host.

 

Mechanism of Hematophagy
There exists a good deal of confusion as to the Candiru's precise methods of prey acquisition. This is due to a conflict between experimental data and the Candiru's natural environment, which is heavily silt-laden and often involves white water, contributing to poor visibility conditions. Therefore it was thought that Candiru had some method of gustation and olfaction, which are common in siluriform fish feeding patterns. However when tested the fish did not respond to increasingly high doseages of urine, and seemed only to track fish visually when the prey swam above the Candiru.
When a prey fish is located however, the candiru navigate into the host's gills and cut a branchial artery in order to utilize the host's blood pressure for a blood supply, being incapable to extract it themselves.