ccache does not recognize environment variables under Fish shell

Hi!
Can you help me understand why ccache isn't recognizing my environment
variables under Fish shell?
I already set CCACHE_DIR to use my tmpfs /tmp/ccache directory:
~ > echo $CCACHE_DIR
/tmp/ccache

But ccache isn't reading it as it shows:
~ > ccache -s
cache directory                     /home/msx/.ccache
cache hit (direct)                     0
cache hit (preprocessed)               0
cache miss                             0
files in cache                         0
cache size                             0 Kbytes
max cache size                       1.0 Gbytes

Any idea? Can I configure ccache with a .conf file? (Already checked the
man page but didn't find any reference)
Best regards,
-Martin