"While he was cleaning the fish tank in his house, he was holding a fish in his hand and went to the toilet for passing urine. When he was passing urine, the fish slipped from his hand and entered his urethra and then he developed all these symptoms."
Lol. He took the fish in with him while he was peeing, and then the fish slipped from his hand -- the 2 cm fish -- and swam up the stream of urine into his urethra. Or his penis was submerged in the water while he was peeing.

This all sounds very plausible.