Below is the unTL;DR, slightly less medical version.
So basically, a 14 year old boy complains of pain, difficulty in passing urine with dribbling and subsequent urinary retention that is 24 hours in duration. On further questioning he told the doctor that while he was cleaning the fish tank in his house, he was holding a fish in his hand when he went to the toilet. When passing urine, the fish slipped from his hand and entered his urethra and he developed the subsequent symptoms.
An X ray and abdominal ultrasound were done, with the ultrasound showing a 1.5cm echogenic object found inside his bladder.
For management a cystourethroscopy was done (i.e. sticking a flexible scope up his penis). A 2cm long dead fish was found inside the bladder. The medical team tried to remove the fish with forceps but was unable to due to its slippery surface. Instead, a rigid ureteroscope with stone graspers was used to remove the fish whole.
Afterwards, the child was asymptomatic and was sent for psychiatric counseling.
This story begs the question, what the fuck was the kid doing with a fish in his hand whilst in the toilet in the first place.
The article itself then goes on about the Candirú or Canero fish, found in the Amazon river. Below is the extract.
"One of the strangest stories from the Amazon was a fish that was urinophilic and could swim up the urethra or into the vagina who urinated while bathing in the Amazon. It was said that this fish, known as candirú [in Brazil; as carnero. Once inside it would eat away the mucous membranes and tissues until hemorrhage would kill it or the host. It was also said that even if one caught the fish by the tail, once in the urethra it could not be pulled out because it would spread itself like an umbrella. in Spanish-speaking countries], was long, thin, and capable of forcing its way into the body's passageways following the trail of urine."