A number of parrotfish species can secrete an odd mucus cocoon in which the fish will sleep through the night. Divers will often find these fish at night, enveloped in a transparent balloon. The discarded cocoon makes an odd sight rolling around the reef the next day.
Even within the same species some fish will use this technique, some will not. It is not known how this behavior is useful to the fish. This very large bullethead parrotfish is sleeping without aid of a cocoon…
