A fisherman has left social media users fascinated after sharing a video of a fish he caught which had another, smaller, fish inside its mouth.

The clip was shared to Instagram, where it has since racked up over 6,300 views and hundreds of comments.

In the video, a catfish can be seen with a smaller haddock hanging out of its mouth.

The fisherman then pulls at the haddock while wearing red gloves and finds only the head remains – with the rest most likely digested by the catfish.

The unusual discovery was made by Roman Fedortsov, 39, from Murmansk, Russia, who has left Instagram users in shock.

He captioned the video: "The catfish had recently eaten haddock, in this case it had been swallowed, but did not have time to digest.

"Very often, when cutting large fish, we find slightly overcooked small fish in their stomachs."⁣⁣

Instagram users were quick to share their thoughts.

“I'm scared again," said one user.

“That was a pretty good last meal for the fish!” said someone else.

“Double R.I.P," joked a third user. [sic]

“I thought you were removing with lobster claws lololol," asked another person. [sic]

"The food chain is too fast :)," added someone else.

"2 for 1," wrote another user, adding a fire emoji.

Another Instagram user shared a similar experience, writing: "As a child, my grandfather got a pike, there were 12 small ones inside.

"All along, exactly like a tin can of sprat."