Honda 2003 Civic Hybrid Owner's Manual page 209

Brake and Clutch Fluid
Clutch System
MAX
MIN
The fluid level should be between
the MIN and MAX marks on the side
of the reservoir. If it is not, add
brake fluid to bring it up to that level.
Use the same fluid specified for the
brake system.
210
Maintenance
Low fluid level can indicate a leak in
the clutch system. Have this system
inspected as soon as possible.