General · EdgepediaSeptember 17, 20265 min read

Candiru (fish)

Candiru (Vandellia cirrhosa Valenciennes, 1846) is a small parasitic freshwater catfish of the family Trichomycteridae, order Siluriformes, native to the Amazon basin, that feeds on the blood of larger fish by entering their gill chambers. It is best known for an urban legend, recorded since the 1820s, that it invades the human urethra; scientific reviews find these reports dubious and conclude the fish poses no meaningful threat to travelers.¹^•²

Key fact	Detail
Scientific name	Vandellia cirrhosa Valenciennes, 1846; GenBank common name candiru; family Trichomycteridae, order Siluriformes¹
Size	Vandellia candirus are usually around 4–8 cm but can reach 20 cm³
Feeding	Wedges itself into the gills of larger fish using spines on its gill covers and feeds on blood; it may remain in the host's gill chamber for up to 145 seconds²^•³
Other names	Also known as toothpick fish, canero, carnero, and urethra fish²^•⁴
Urethra legend	Reports since the 19th century are disputed; recent research shows the fish hunts by sight and is not attracted to human urine²
Documented case	The most recent claimed urethral invasion, published in 1997, involved a fish of 133 mm removed endoscopically; its veracity has been doubted²
Travel medicine	A systematic review concluded there appears to be no need to consider the candiru in health advice for travelers to the Amazon⁵

Taxonomy and what counts as a candiru

The name candiru is applied loosely. In the strict sense it refers to Vandellia cirrhosa, the single species to which the infamy of urethral penetration is restricted.¹^•⁶ In a broader sense, "candirus" are a notorious, polyphyletic (group descended from multiple unrelated ancestors, not one lineage) assemblage of South American catfishes defined by specializations for feeding on carrion or on the living blood, scales, or skin of other vertebrates. Candirus belong to two clades that are only remotely related to each other: Cetopsinae, a subfamily within Cetopsidae, and the pair of sister subfamilies Stegophilinae and Vandelliinae, both placed in Trichomycteridae.⁷ The carrion-eating whale candirus (Cetopsis species) and the scale-feeding stegophilines are sometimes conflated with the blood-feeding vandelliines under the shared common name, despite the group's polyphyly.⁷^•³

The genus name Vandellia honors Domenico Vandelli (1735–1816), an Italian-Portuguese naturalist who worked in Lisbon and described Brazilian fauna.⁸

Feeding biology

Vandelliine candirus are obligate blood-feeders as adults. Vandellia cirrhosa uses spines on its gill covers to wedge itself into the gill chambers of larger fish, where it rasps blood from the gill arteries; the two most extensively studied Vandellia species feed this way, and a feeding fish shows an engorged belly, with blood leaking from the host's gill opening.²^•³^•⁷ A visit to the gill chamber can last up to 145 seconds.³

Hosts are not defenseless. FishBase records that the host fish Colossoma macropomum can hamper a candiru's attack by pressing it under the membranous gill-cover flap, or by using a pectoral fin to press it against the flank or sweep it from the gill-cover edge.⁹

The urethra legend and the evidence

Origins of the story. In 1829 the German biologist and explorer Carl Friedrich Philipp von Martius traveled to Brazil and was told by natives about candirus invading human urethras; local men used protective coverings and even tied ligatures around their penises before entering rivers. Martius hypothesized that urine odor attracted the fish, because the fish's primary prey emit urea from their gills. In 1855, during an expedition in the Araguaia region, the French naturalist Francis de Laporte de Castelnau was told by local fishermen that candirus "spring out of the water and penetrate into the urethra by ascending the length of the liquid column", a claim that defies the laws of physics. By 1930, reports described candirus entering the vagina, but not the male urethra.²

Why the story fails. Recent research shows the fish hunts by sight and is not attracted to human urine, and a review of the medical literature found no robust evidence that vandelliine candirus react to ammonia or blood in water.²^•³ Ichthyologists note that to the extent the alleged behavior has any truth, it is exclusively associated with the vandelliine genus Vandellia, and many of the reports are dubious.⁷

The 1997 case. The most recent claimed urethral invasion was published in 1997: the patient reported urethral bleeding, difficulty passing urine, and fever three days after an attack by a small fish while urinating into a river. Cystoscopy showed a fish lodged in the anterior urethra, and it was removed endoscopically in a filmed procedure. Doubts about the report's veracity rest on the size of the extracted fish (133 mm), the history given by the patient, and the lack of incentive for a candiru to invade a urethra.²

Practical conclusion. A 2013 review in the Journal of Travel Medicine concluded that until evidence of the fish's threat to humans is forthcoming, there appears to be no need to consider the candiru in health advice for travelers to the Amazon.⁵ Medical summaries likewise state that the widely repeated stories are based more on myth than strong medical evidence, and that confirmed human injuries appear to be very rare.¹⁰

Other candirus and human medicine

Not all fish called candiru are blood-feeders, and some do interact with humans in documented ways. The carrion-eating whale candirus Cetopsis candiru and Cetopsis coecutiens may attack live fish in gillnets and occasionally humans; their bites cause deep lesions on human corpses and are strong enough to leave circular marks on skull bone.³ A human-biting vandelliine candiru from a scientifically undescribed genus and species has also been reported, fastening to a victim's body with specialized teeth and feeding on blood, leaving an elliptical wound similar to the lesions V. cirrhosa inflicts on the gill arteries of fish hosts.³ Accounts of candirus' impact on people are, in several cases, dubious or imprecise even in scientific reports.³

References

Topic: Encyclopedia › Life and health › Animals › Vertebrates › Fish › Ray-finned fish (Actinopterygii)

Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026

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