Alan Bellows calls it The Terrifying Toothpick Fish, but some of us know it as the dreaded candirú:
Though the candirú is a parasite, humans are not among its viable hosts. It lingers in the murky darkness at the river’s bottom, quietly stalking its neighboring fish. Light is scarce in the soupy deep, but the candirú does not need to see… it can taste the traces of urea and ammonia that are expelled from breathing gills.The tiny hunter shadows its prey, almost invisible due to its translucent body and small size. When the target fish exhales, the candirú detects the resulting flow of water and makes a dash for the exposed gill cavity with remarkable speed. Within less than a second it penetrates the gill and wriggles its way into place, erecting an umbrella-like array of spines to secure its position.
Unconcerned with the host’s panicked thrashing, the firmly anchored parasite immediately nibbles a hole in a nearby artery with its needle-like teeth, feasting upon the bounty that gushes forth. Within two minutes the candirú’s belly is swollen with the blood of its victim, and it retracts its gripping barbs. Though it may seem that the exploited host fish has escaped, its injuries are so extensive that chances of survival are grim. Meanwhile the victorious attacker slinks back into the river’s dark places to digest its meal.
There are many troubling stories regarding human run-ins with the candirú, though until recent years these were not given much credence by the medical community. It is not uncommon for people swimming or bathing in the river to urinate in the water, an action which creates tiny water currents that are rich in urea and ammonia. It seems that the tiny, slender catfish cannot always distinguish a urinating human from an exhaling fish gill, and on occasion it will attempt its trademark high-speed attack on some unfortunate soul.
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