The species in this genus are the most well-known of the parasitic catfishes also known as candiru, known for their alleged habit of entering the human urethra.

V. cirrhosa enters the gill chambers of larger fish to suck blood.

Some kind of valve or sphincter is likely present to prevent reflux of ingested blood.

The time required to engorge itself with blood and leave the host's gill chamber ranges from 30–145 seconds.

Some host fish species (Colossoma macropomum) are able to hamper the attacks of V. cirrhosa by pressing the fish under the bony gill-cover flap, or by using its pectoral fin to press it against the flank or to sweep it from the gill-cover edge.