be another different kettle of fish

be another/a different kettle of fish

if you say that something or someone is a different kettle of fish, you mean that they are completely different from something or someone else that has been talked about Andy was never very interested in school, but Anna, now she was a completely different kettle of fish. I'd driven an automatic for years but learning to handle a car with gears was another kettle of fish altogether.

See also: another, different, fish, kettle