The common name candiru is given to the genus Vandellia, comprising a group of miniscule catfish that possess physical features suited to preying off the blood of live fish (Breault, 1991). Given their nocturnal tendencies and habitation of murky waters, these fish rely on chemoattractants such as urea or ammonia to locate ammonotelic prey items, those that excrete nitrogenous wastes (Spotte et al., 2000). Specimens of this genus have become notorious for their ability to penetrate various orifices, including those of humans, in their search for food (Gudger, 1930).
V. sanguinea are indigenous to the neo-tropical waters of South America, specifically those of the Amazon, Orinoco, and Essequibo River basins (Ferraris, 2007). They have been banned from importation in many areas on account of their threat to the native aquatic fauna (Shafland, 1986).
V. sanguinea can be recognized by their thin, elongate bodies which are scaleless. They lack adipose fins, and their dorsal fins are posteriorly located (Borin and Martins-Santos, 1999). Other defining features include the presence of a median premaxilla, reduced premaxillary dentition, small sensory barbels angled to the mouth, and the presence of sharp, claw-like teeth used to access host arteries.
V. sanguinea are parasitic fish with backwards oriented spines on their opercula, or gill flaps, that facilitate attaching themselves onto prey items to feed; however, they lack the dorsal and pectoral fin spines characteristic of other catfish (Baskin et al., 1980). They grow to approximately 8.4 cm (standard length for males), though some reports of 15 cm have been documented (Piper, 2007). They are drab-colored and translucent with minor dorsal pigmentation, enabling camouflage in murky waters and the substrate. V. sanguinea also possess small, flattened heads with short sensory barbels and shiny bellies that engorge when filled with blood (Eigenmann, 1917).
This species is distinguished by the following traits: maxillary barbel extending to the tip of the interopercular spines; 0.5 mm long lower barbel and 2.5 mm long maxillary barbel; two, flat, recurved teeth on the end of the maxillary concealed just in front of the barbel; five premaxillary teeth diminishing in size from the central tooth; mandibles widely separated from each other, each with approximately five minute teeth; teeth concealed by the lip; five spines in the main row of the interopercle, the middle ones directed backward; distance between origin of ventrals and base of middle caudal rays 2 times its distance from the snout; about five spines in supplementary rows; five spines in the main row of the opercle, about ten in supplementary rows; origin of anal fin behind the origin of the dorsal fin; the last dorsal ray over the middle of the anal ray; distance between origin of dorsal and base of middle caudal rays 2.8 times its distance from the snout; and caudal fin truncated with numerous accessory rays (Eigenmann, 1917).
V. sanguinea can be found in the freshwater rivers of South America. Although capable of swimming freely, as observed when scavenging for prey, V. sanguinea tend to stay buried under the muddy substrate or seek shelter under rocks or logs during the day (Zuanon and Sazima, 2003). They can be found at a variety of altitudes, from flooded lowland forests to high-elevation streams in the Andes (Fernandez and Schaefer, 2009).
Vandelliine trichomycterid catfishes, including V. sanguinea, attach to hosts when feeding but disengage when sated. As a result, their parasitism does not function as a means for travel. However, species of the genus Paracanthopoma, which are in the same family (Trichomycteridae) as Vandellia, have been found to ride pimeloid catfish in the upper Amazon by latching onto the caudal, dorsal, or pectoral regions of the these large, migrating fish (Zuanon and Sazima, 2005). While both V. sanguinea and P. parva possess morphological features that enable them to exploit the blood of their hosts, the stomach contents of P. parva contain only meager amounts of blood, and they adhere to regions of larger catfish that are not blood-rich, indicating they utilize these larger creatures for purposes of travel, unlike their Vandelliine counterparts (Zuanon and Sazima, 2005).
The candiru do not discriminate among potential hosts when feeding, and there are no known predators of the candiru. Natural hosts of V. sanguinea include characins, cichlids, and larger silurids such as pimelodids and doradids (Spotte et al., 2000). Some species of fish, including the tambaqui, are able to close the operculum on the side being attacked while ventilating through the other side, effectively denying the candiru access to arterial blood (Zuanon and Sazima, 2003).
Life History and Behavior
V. sanguinea are obligatorily hematophagous, preying solely on the blood of their hosts. Attracted by the scent of urea, the parasites proceed to attack the dorsal or ventral arteries of the gills by wedging themselves under the gill flaps of hosts, erecting their dorsal and opercular spines to secure their position, accessing the blood supply via dagger-like teeth, and engorging themselves on the meal before disengaging their hosts (Baskin et al., 1980). They are capable of obtaining a full meal of blood anywhere from 30 to 145seconds (Zuanon and Sazima, 2005). Small scratches within the gill filaments of hosts indicate that V. cirrhosa bite the medial and proximal area of the gill filaments and simply allow the pressurized arterial blood to flow into their alimentary canals (Zuanon and Sazima, 2003). Incidents of a related species, V. cirrhosa, swimming up human urethras have been reported as these fish mistake the chemicals released in urine as natural waste products of prey items (Fernandez and Schaeffer, 2009).
Molecular Biology and Genetics
The status of V. sanguinea is currently not threatened. Bans of this species in many countries have helped keep them localized indigenously. Some states require the possession of a Wild Animal License in order to distribute or harbor these creatures (Shafland, 1986).
The populations of V. sanguinea are stable and are not endangered by either natural or artificial means; they are also deemed a low vulnerability species (Torres and Sa-a, 2010).
Currently, V. sanguinea is neither endangered nor threatened. They have few natural predators, and the stigma of entering human orifices has allowed these fish to remain relatively unexploited (Torres and Sa-a, 2010).
Relevance to Humans and Ecosystems
Although the candiru currently provide no benefits for humans either commercially or as a food source, there have been reports of detrimental interactions of candiru entering the urethras of unwitting bathers. Upon entry, they can cause extreme pain in the affected region by erecting their opercular spines and lacerating the mucus membranes of the urethras (Gudger, 1930). The most common treatment is amputation of the affected area; however, if left unattended, death from shock and blood loss can ensue. A native herb has been found to digest the spines of the catfish, allowing for easier evacuation of the parasite (Breault, 1991).
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