If you're a fish, there's nothing more irritating than a blood-sucking parasite stopping you from having a good night's sleep. That's exactly why Parrotfish go to extreme lengths to prevent this from happening.Every night before going to sleep, Parrotfish secrete a mucus cocoon that envelops their entire bodies with a protective biopolymer – something similar to a mosquito net. The genius thing about it is that this net lets small molecules to pass through, but blocks anything larger (i.e. bloodsucking parasites). Oh, and the whole process only takes the Parrotfish around 2.5% of its daily energy budget. Not too pricey for a good night's sleep!