a different kettle of fish

US /ə ˈdɪf.rənt ˈket̬.əl əv fɪʃ/
UK /ə ˈdɪf.rənt ˈket̬.əl əv fɪʃ/
"a different kettle of fish" picture
1.

something that is completely different from something else previously mentioned

:
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I thought I could handle the new project, but it turned out to be a different kettle of fish.
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Dealing with clients is one thing, but managing a team is a different kettle of fish.
:
a fine kettle of fishkettleput the kettle onfishfishingdifferentdifference