humans Sting Like other stingrays, members of the family Potamotrygonidae have a venomous stinger on the tail (although it is harmless and vestigal or even absent in Heliotrygon). There are generally one or two stingers, and they are periodically shed and replaced. They are some of the most feared freshwater fishes in the Neotropical region because of the injuries they can cause. In Colombia alone, more than 2,000 injuries are reported per year. Freshwater stingrays are generally non-aggressive, and the stingers are used strictly in self-defense. As a consequence injuries typically occur when bathers step on them (injuries to feet or lower legs) or fishers catch them (injuries to hands or arms). In addition to pain caused by the barbed stinger itself and the venom, bacterial infections of the wounds are common and may account for a greater part of the long-term problems in stinging victims than the actual venom. The stings are typically highly painful and are occasionally fatal to humans, especially people living in rural areas that only seek professional medical help when the symptoms have become severe. In general, relatively little is known about the composites of the venom in freshwater stingrays, but it appears to differ (at least in some species) from that of marine stingrays. There are possibly also significant differences between the venoms of the various Potamotrygonidae species. Due to the potential danger they represent, some locals strongly dislike freshwater stingrays and may kill them on sight. A study at the Butantan Institute, São Paulo, Brazil, revealed that the freshwater stingray venom changes according to sex and age. With the composition varying even between individuals of the same species. Each time the environment changes, the feeding of the stingray changes, leading to changes in the composition of toxins and toxicological effects. There is no specific antidote or treatment for freshwater stingray. Symptomatology Accidents occur when the rays are stepped on or when the fins are touched, the defensive behavior consists of turning the body, moving the tail and introducing the stinger into the victim. Generally, stingers are inserted into the feet and heels of bathers and the hands of fishermen. Initial symptoms include severe pain, erythema and edema, then necrosis occurs which results in sagging tissue in the affected area and forms a deep ulcer, which develops slowly. Systemic complications include nausea, vomiting, salivation, sweating, respiratory depression, muscle fasciculation and seizures. Once the stinger