A female who lays there seemingly lifelessly during sexual intercourse.
Ryan: Hey Jonny Boy, heard you porked that girl Charline, how was she?
Jon: Dude, girl's a total stalefish. Thought I was fucking a corpse.
Female who is average in skills and activity when it comes to sexual intercourse.
She may still be a bottom feeder, but she definitely shows signs of life unlike a stalefish. However, she isn't quite up to par with salmon status.
Kevin: Rumor has you you and Kate did the nasty last weekend? How is she?
Jon: Keep this on the DL, but she's a flounder. Not bad, but nothing too special.
Female who is extremely talanted and active during sexual intercourse.
Opposite of a stalefish, and better than a flounder.
Justin: Dude, you did the horizontal hokey pokey with Jessica? That girl has to be a salmon.
Jon: My man, girl is a salmon at it's finest. Rode me like a stallion.