The clips, published on Facebook, show Sam Murray, 19, stuffing a friend’s family pet into his mouth at a party.
Sam, from Oxgangs, then chews up the fish and spits it out - to the screams and encouragement of his friends.
Mum Carol, 35, said she was furious about the stunt, adding: “I told him it was a stupid thing to do. Everyone knows what social media is like - you share one thing and it just goes mental.”
The first video recorded at the house party begins with Sam lying on a bed surrounded by pals in the early hours of Sunday morning.
Seconds later he is seen shoving something in his mouth.
The party hostess is then heard screaming: “Why have you got my goldfish in your mouth?”
Another partygoer in the background said: “That’s minging” - but a male voice yells: “You’re a legend.”
In a second video, posted seconds later, Sam spits out the maimed pet’s remains.
He holds out his hand to the person holding the camera and boasts: “Look, there’s its eyeballs”.
Horrified Twitter users condemned the scenes after the clips were uploaded on Sunday.
Luke Campbell said: “I actually feel sick”, while Melissa Roy wrote: “What a disgusting boy”. Becca Howard added: “I’m boking. That’s rank.”
Animal welfare officers are now investigating the two clips of the cruel prank.
John Robins, secretary of charity Animal Concern, said: “It is a terrible way to kill an animal. These stunts aren’t funny. It’s a criminal offence and it’s quite right someone should face prosecution.”
Causing an animal unnecessary suffering carries a maximum penalty of a year’s jail and a £20,000 fine.
Last July Callum Clatworthy-Robins, of Port Talbot, South Wales, was fined £100 for eating a goldfish he won at an amusement stall.
He was given it in a bag as a prize, but swallowed it whole after leaving the funfair.