I forgot the name of a monster

[FunnelCake]

Hey Guys!

I saw an old post where someone asked for a forgotten name of a monster.
Well that happened to me too.
It wasn't part of any roleplaying games that I played so far but I hope you guys can still help.

All I remember that it was a sea serpent that could change to a fish and when a fisherman cath the fish It would transform back to his giant serpent form.
Probably Its from a Norse mythology but I'm not sure :\

Forgive me for my grammar mistakes.

Thanks

Edit: I found it! It was Cirein-Cronin!

[knag]

Hey Guys!

All I remember that it was a sea serpent that could change to a fish and when a fisherman cath the fish It would transform back to his giant serpent form.
Probably Its from a Norse mythology but I'm not sure :\



Reminds me of the myth of Thor catching Jormungandr. Your sea serpent is Celtic; I wonder if there is any connection between the Norse and Celtic myths of fishing for giant sea serpents...