Most all fish spend time in an energy-saving state (rest), it's kind of different than sleep though, they "sleep" differently than other land animals... Many fish, like Bass and perch, rest on or under logs at
night. Coral reef fish active in the day, hide and rest in crevices
and cracks in the reef to avoid being eaten at night. The resting behavior of fish is very different from their behavior the
rest of the day. Many minnows, for example, which are very active in
schools during the day, scatter and remain motionless in shallow
water at night. Many fish "rest" or "sleep" during the day and are
active at night instead, but almost all fish sleep. There are some animals that never stop swimming, like many species of
shark, however, they HAVE to keep moving to push water through their mouths in order to breathe...they might sleep while moving, but I don't know.