The Candiru fish, Vandellia cirrhosa, is a small, parasitic freshwater catfish native to the Amazon basin. Often called the “vampire fish,” its notoriety stems from accounts of it invading human orifices. It belongs to the family Trichomycteridae, a group of catfishes known for specialized feeding habits. The widespread fear it inspires is rooted in a sensationalized myth.
Identification and Natural Habitat
The Candiru is a physically distinctive fish with a diminutive, elongated, and eel-like body. Most specimens measure less than two inches long, though some reach up to five inches. Its small size and translucent body make the fish difficult to spot in the murky Amazonian waters.
Its head is slightly flattened, featuring short sensory barbels and backward-pointing opercular spines on the gill covers. These sharp spines anchor the fish to its host during feeding. The Candiru is found exclusively within the Amazon and Orinoco River basins, including Brazil, Bolivia, Peru, and Ecuador. It prefers a benthic lifestyle, inhabiting the bottom of shallow, slow-moving, acidic waterways, often remaining buried in the riverbed.
The Candiru’s Unique Feeding Mechanism
The Candiru is a parasite that feeds exclusively on the blood of larger fish, such as catfish or characin. It locates a host using both visual and chemo-sensory cues. Modern research indicates the fish is not specifically attracted to chemicals expelled through the host’s gills.
Upon locating a host, the Candiru swiftly attempts to penetrate the gill chamber, forcing its way beneath the operculum. Once inside, it erects its backward-pointing opercular spines, anchoring itself firmly. The fish then uses needle-like teeth to make an incision in a major artery.
The host’s own blood pressure forces the blood directly into the parasite’s gut. This engorgement process is rapid, with a single blood meal typically lasting between 30 and 145 seconds. After feeding, the Candiru detaches to sink and burrow back into the river bottom.
Separating Fact from Fiction: The Human Invasion Myth
The reputation of the Candiru rests on the myth that it swims up the human urethra or other orifices. This narrative suggests the fish is attracted to human urine in the water. However, scientific analysis has discredited the idea that the fish is drawn to urine or that it commonly attacks humans.
Studies show that the Candiru hunts by sight and is not strongly attracted to the chemical composition of human urine. Fluid dynamics experts consider it impossible for a small fish to swim against the force of a urine stream. The urethra is a tightly constrained tube, and forcing entry is beyond the fish’s physical capabilities.
The myth is often supported by a single, controversial 1997 case in Brazil, where a urologist claimed to have surgically removed a Candiru from a man’s urethra. Investigation revealed inconsistencies, including discrepancies in the fish’s size and the alleged mechanism of entry. The preserved specimen was too large to have easily entered the urethra, and the claim that the fish “chewed” through tissue was inconsistent with its dentition.
Outside of this disputed case, there is a lack of verifiable clinical evidence to support widespread human invasion. The consensus among biologists is that if a Candiru enters a human orifice, it is a rare, accidental anomaly, not a deliberate parasitic attack. The risk to bathers is extremely low.