The Amazon basin is home to the candiru, a small, notorious fish. Primarily found in South America’s vast river systems, it has gained a fearsome reputation. Its unique characteristics and the legends surrounding its behavior spark widespread curiosity.
Unveiling the Candiru
The candiru belongs to the family Trichomycteridae, a group of parasitic freshwater catfish, with Vandellia cirrhosa being the most commonly referenced species. These fish are typically small and slender, often described as eel-like, with most specimens measuring between 2.5 to 17 centimeters in length, though some reports indicate lengths up to 40 centimeters. Their bodies are scaleless and translucent, making them difficult to spot in the turbid waters of their habitat.
Physical features of the candiru include barbels near their mouths, equipped with minute, needle-like teeth, and short, backward-facing spines on their gill covers. These spines are present in all trichomycterids and are used for anchoring. Candiru primarily inhabit the shallow, slow-moving, and often acidic waterways within the Amazon and Orinoco river basins, including countries like Bolivia, Brazil, Colombia, Ecuador, and Peru. They spend much of their time burrowed in the muddy or sandy riverbed, emerging mainly to feed. While their eyesight is limited, they possess a lateral line system, which helps them detect movements in the water.
The Truth Behind the Legend
The candiru’s notoriety stems from its actual parasitic behavior and the exaggerated myths surrounding human interactions. In its natural environment, the candiru is hematophagous, meaning it feeds on the blood of other fish. It locates potential hosts, often larger fish, using visual and chemical cues before entering their gill chambers. Once inside, the candiru attaches itself to the host’s ventral or dorsal aortal arteries, using its opercular spines to secure its position and ensure blood flow.
The fish does not actively “suck” blood; instead, the host’s blood pressure pumps blood directly into the candiru’s mouth. A single feeding session is usually brief, lasting between 30 to 145 seconds, after which the candiru detaches and burrows back into the river bottom to digest its meal. While candiru can cause inflammation and hemorrhage in their fish hosts, they rarely cause death.
The widely circulated legend of the candiru swimming into human urethras is largely anecdotal and scientifically debated. Accounts of such incidents have existed for centuries, but robust scientific evidence supporting voluntary entry into human orifices is lacking. The most publicized modern case from 1997 in Brazil remains highly controversial due to inconsistencies in the victim’s account and the specimen’s condition.
Research indicates that candiru hunt by sight and show no attraction to urine or other chemical attractants. The common belief that they are lured by human waste streams is refuted. The physical dynamics of swimming against a urine stream also make such an event highly improbable. While rare, incidental entries into human orifices might occur by mistake, it is not the fish’s typical or natural feeding behavior.