FISH is a word used by trans women to describe a trans
woman as very feminine- indistinguishable from a cis
woman.
it was initially a slur that described cisgender
woman... it was used by men who associated the smell of a
woman's vagina with fish. the word is not really used in this context anymore. instead, it started being used by gay men and trans women to describe drag queens that truly embodied cis femininity and eventually came to mean what it means today. when trans women call each other fish, they are complementing each other, by comparing each other to cis women.