The meaning of a cold fish is someone that is reserved, aloof, unemotional and someone who also lacks warmth or cordiality in their interactions with other people.
A cold fish implies a lack of emotional expressiveness and also a tendency to be unapproachable or distant.
A "cold fish" does not readily display their feelings or their emotions and often appears stoic or detached.
A cold fish may also keep others at arm's length and not readily engage in friendly or warm interactions.
And they may also not be very welcoming, sympathetic or kind in their demeanor.
The idiom "a cold fish" is believed to have originated in the 19th century.
And it also has been noted as a mistranslation of a Latin phrase that means "stubbornly they turn".
And other phrases that convey similar meanings to "a cold fish" are "icy person" or an "unemotional person".
A cold fish in bed refers to a sexual partner that who during sex, lacks vigor or emotional reciprocity.