August 15: Fish

Most fish spend time in an energy-saving state that can be called ‘rest’. Being ‘asleep’ means different things to different fish. Some fish are motionless in the water during the night. Others don't appear to sleep at all (they rest against rocks, bracing themselves with their fins). Some freshwater fish swim up under a log or river bank for shelter during the day. Fish can't close their eyes; none of them have eyelids.