Medical importance of candiru catfishes in Brazil: A brief essayDear Editor,
The type of catfish referred to as candirus, is a member of the Trichomycteridae and Cetopsidae families1,2. The subfamilies Vandelliinae and Stegophilinae (Trichomycteridae) and Cetopsinae (Cetopsidae) are relevant to human medicine, including forensics1,2,3,4. Herein, we present a brief essay on candirus and their relationship with human health and death. We examined published accounts and used our personal observations on the subject.
Candirus of the genusVandellia are small (usually around 4-8 cm but can reach a size of 20 cm), have an elongated body (Figure 1A), and their mouths contain sharp, needle-like teeth. The two most extensively studiedVandellia species feed on blood from the gill arteries of larger fish (Figure 1B). These candirus may remain within the gill chamber of the fish host for up to 145 seg5. There is no robust evidence that vandelliine candirus react to ammonia or blood in water6, but they allegedly enter the human urethra or other natural orifices to feed on blood7,8,9. However, such cases are disputed due to the apparent lack of solid evidence9.
However, cases of attacks on humans by a vandelliine candiru that inflicts wounds on the body of the victim have emerged recently. This candiru was identified to be a part of a scientifically undescribed genus and species2 and is referred to here as the human-biting candiru. This candiru fastens itself to the victim’s body with its specialized teeth (and perhaps using interopercular spines) and feeds on blood (Figure 2A). The fish is difficult to remove from the victim (Figures 2B andD) because of the forceful bite exerted by the powerful head muscles.
Upon forceful removal of the fish, the wound bleeds for a while (Figure 2D). The lesion caused by human-biting candiru is elliptical, similar to the wound inflicted by the blood-feedingVandellia cirrhosa on the large arteries of its fish hosts5.
Candirus of the subfamily Stegophilinae are small-sized fishes (about 10-15 cm) that semi-parasitize large fishes10. They fasten to their victim with the disproportionally expansible sucking disc-like mouth, bite, and spread the opercular and inter-opercular spines into the wound to remain attached, scraping off mucus or scales10,11 or taking blood12. Within the Stegophilinae subfamily, the candiruPareiodon microps stands out as a species of forensic importance due to its carrion-eating habits2,11. This candiru is slender and long (Figure 1C) and is unlikely to be confused with the stouter carrion-eating whale candirus, despite the shape of its mouth (Figure 1D). This stegophiline candiru joins the whale candirus while feeding on dead vertebrates2,13, which may include humans.
The whale candirus of the subfamily Cetopsinae are unrelated to vandelliine candirus1. Cetopsine candirus are stockier and larger (up to about 30 cm) than vandelliine and stegophiline candirus (Figure 1E). Only two of about 35 species of whale candirus are carrion-eaters that tear off chunks of tissue with their specialized, pointed, razor-sharp teeth on the mandible1,14,15. These fishes penetrate the bodies of drowned or otherwise dead animals, including humans, and feed on viscera and musculature1,15. Whale candirus may attack live fish in gillnets and occasionally, humans1,7. Human corpses attacked by whale candirus have round deep holes on the body surface, which correspond to exit or entry holes1,15.
The two carrion-eating whale candirus display different behaviors when feeding1.Cetopsis candiru bites and makes a rotational movement along its vertical axis, tearing off an almost round piece of tissue and tunnels its way into the corpse7. Then, it proceeds to enter the body cavity, eating the corpse from the inside out1,15.
This candiru species display a feeding frenzy that may involve tens to hundreds of individuals1,7. However, the whale candiruCeptosis coecutiens bites quickly and tears off chunks of tissue and then withdraws to attack again1. Attacks by these twoCetopsis species cause deep lesions on human corpses, and the bite of the whale candirus is so strong that it leaves circular marks even on the skull bone of the victims15.
Feeding frenzies ofC. candiru on dead vertebrates may be joined by the carrion-eating catfish piracatinga, also known asCalophysus macropterus, of the family Pimelodidae7,13. This long-whiskered catfish also has razor-sharp teeth, appropriate to tear pieces of flesh off dead bodies, including those of humans15.
Finally, it is important to remember that reports on candirus and their relationship to human health and death are biased by imprecision, second- and third-hand accounts, misconceptions, and folk tales1,2,7,8,9. Due to the above-mentioned biases, several accounts of the impact of candirus on people are dubious or at least imprecise, even in some scientific reports and books.
