The Candiru (Vandellia cirrhosa) is a small, parasitic catfish native to the freshwater systems of South America. This slender, typically translucent fish has gained a sensationalized reputation far exceeding its size. To understand the Candiru, it is necessary to focus on its actual environment and biology. This species is endemic to the Amazon basin, and its habitat dictates its behavior.
Geographic Range: The Amazon Basin
The Candiru’s distribution is vast, encompassing the entire Amazon River drainage basin in South America. This area includes parts of several countries: Brazil, Peru, Colombia, Ecuador, and Bolivia. The fish is not restricted to the main Amazon channel but thrives throughout the network of tributaries, streams, and connecting waterways. Candiru are also found in the related Orinoco River basin, expanding their geographic range across this massive drainage system.
Specific Aquatic Habitat
Within the expansive Amazon basin, the Candiru seeks specific micro-environments. It is a demersal fish, meaning it is bottom-dwelling and spends much of its time burrowed in the riverbed. This species prefers shallow, slow-moving waterways with a soft substrate. Candiru are commonly found over sandy or muddy bottoms in turbid, low-visibility waters. They inhabit small streams and tributaries, often referred to locally as igarapés. This concealed habitat allows the translucent fish to hide from predators and wait for its host fish.
Feeding Habits and Notoriety
The Candiru is a hematophagous micropredator, meaning it feeds on blood. Its survival depends on locating and parasitizing larger fish abundant in its preferred turbid, shallow waters. The fish enters the gill cavity of a host fish, often a larger catfish, by forcing itself under the gill cover. Once inside the gill chamber, the Candiru uses sharp spines to anchor itself to the host’s tissue, typically biting into the aortal arteries. The host’s blood pressure pumps the blood directly into the Candiru’s gut, and a single blood meal may last from 30 to 145 seconds. The fish locates its hosts using a combination of visual and chemo-sensory orientation.
The notoriety of the Candiru stems from historical, though highly disputed, accounts of it entering the human urethra. Scientific studies have shown that the fish is not attracted to chemical cues like urea or ammonia, which are present in urine. Documented cases of human parasitism are extremely rare and lack robust evidence. The fish’s true biological purpose remains its parasitic feeding on larger fish in the Amazon’s murky, bottom-dwelling habitats.