Ask Asta: Do fish sleep?

Asta loves exploring and studying the exciting world under the sea. Each week, she will attempt to learn and answer her reader's most burning marine science questions, and provide some resources that help turn the question into a lesson plan!



This weeks question comes from Ilan, age 5:


   "Do fish sleep? How?" 

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 Fish may not curl up in a comfy bed like humans do, but they still make time for rest and refreshment. They can't get any shuteye though because fish don't have eyelids!

•  Some fish rest by going into an almost trance-like state, in which they rest while floating almost motionless (or moving just their fins) in the water column. Some even rest on the sea bed, or build small nests out of pebbles or soft debris. Fish can rest at any time, day or night, but most fish are diurnal, like humans are. 
• Resting or 'sleep' means something slightly different in fish: it is usually defined as long periods of stillness, with little eye movement, slower heart rate and breathing patterns, and a decrease in response to touch or sound.

• If you have an aquarium at home, you might notice that sometimes your fish float motionless for long periods of time. Some scientists believe that when fish are resting, they are using only half of their brain power to breathe, stay away from objects and other fish around them, and detect predators.
  

• Other fish have to keep swimming-even when they are resting! These fish often use what is known as "ram ventilation", meaning they have to keep swimming in order to get water through their gills to breathe. Some cartilagenous fish, like certain sharks, are thought to go into "autopilot" mode when they are resting, meaning they swim along undisturbed until they come across something that looks or smells tasty.  Then, they wake up and start using all their senses to help them hunt.

• Some sharks like to have slumber parties, like the White Tip Reef Shark. These beautiful predators return to the same spot very regularly, and stack together with other sharks while they rest.  They tend to congregate in areas where they oxygen content of the water is high, so that they don't need to swim to get the oxygen they need!

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A white tip slumber party! From DutchSharkSociety.org

Photo of a Zebrafish. Taken from Wikipedia commons.

• Zebrafish are being used as models to better understand sleep disorders. Dr. Emmanual Mingot and Dr. Toke Yokogawa led a study using zebrafish to determine how a protein called hypocretin affects sleep patterns. 
• The research team compared the length and times of zebrafish naps between fish that produced the Hypocretin and fish that  had been genetically modifed so that they did not produce the protein. The reserachers discovered that the fish that did  not produce Hypocretin slept 30% less often and for only about half the time as fish who did produce Hypocretin.  This research may eventually  help scientists understand sleep problems such as narcolepsy and insomnia!
  

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•  When it's time to rest, Parrot fish produce a mucus sleeping bag which wraps around them and keeps them protected while they sleep.
• There are many theories as to why Parrot fish need a sleeping bag. Some believe the bag is used  as an early warning system to protect the fish from predators, like the moray eel. Others think it has to do with protecting the Parrotfish from dust or sea debris floating around in the water. 
• Alexandra Grutter from the University of Queensland theorizes that the sleeping bag is used to prevent attack from Gnathic isopods, a type of blood sucking crustacean. Take that, vampire crabs! 

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There are still plenty of unanswered questions about fish sleep. Fish all seem to sleep slightly differently. 


Maybe this would be a cool subject to research as a biologist! What do you think this knowledge could be useful for?



References:

• Bite by a Shark blog.December 18, 2013. "Do Sharks Sleep?" Accessed February 20, 2014. http://bitebyashark.com/interesting-facts/do-sharks-sleep/
• Seagrave, W. March 4, 2008. "How do Fish sleep?" Big Question Blog. Accessed February 20, 2014.https://bigquestion.wordpress.com/2008/03/04/how-do-fish-sleep/


• Yong, E. November 17, 2010. "Parrotfish sleep in a mosquito net made of mucus." Not Exactly Rocket Science Blog. Discovery Magazine. Accessed Feburary 20, 2014. http://blogs.discovermagazine.com/notrocketscience/2010/11/17/parrotfish-sleep-in-a-mosquito-net-made-of-mucus/#.UwZFCJVVots
  
• Life's Little Mysteries Staff. October 2, 2012. "Do fish sleep?" Live Science Blog. Accessed February 20, 2014. http://www.livescience.com/32162-do-fish-sleep.html
• Reebs, Stephan. "Do fish sleep at night?" Queen's University Publication. Accessed February 20, 2014.http://professeur.umoncton.ca/umcm-reebs_stephan/files/umcm-reebs_stephan/wf/wf/pdf/FMA%20Do%20fish%20sleep.pdf