I was looking back at pictures from one of my old night dives in Belize, and I saw a photo of a parrotfish encased in a mucus sleeping bag, which got me wondering: literally why would they want to make these sleeping cocoons? This is the question I’m focusing on for this week’s blog!
Parrotfish are members of a subfamily called Scaridae, which is a subset of the wrasse family, Labridae. They get their name from their beak-like mouth, which is made up of teeth that are fused together.
There are around 100 species of parrotfish, but I will only be talking about one. The fish I will be focusing on is the queen parrotfish (Scarus vetula), a vibrant and eccentric blue fish living on reefs, mainly in the tropical area of the West Atlantic Ocean, the Caribbean Sea, and the Southern Gulf of Mexico. Their main diet consists of the algae found covering coral polyps, making them a vital part in the maintenance of coral health. Not all species of parrotfish choose to secrete a mucus bubble if they developed other, less energy taxing methods of defense during rest, but this specific species did! This is an example of facilitative behavior, meaning it is an optional behavior that develops in response to certain environmental factors.
The queen parrotfish sleeping in its cocoon is quite a rare sight to see while diving, since they choose to make them in the cracks and crevices of the reef. They excrete a mucus from specialized glands located right behind their gills (or mouth, there were a lot of opposing articles) until it encases their entire body, which takes around 30 to 60 mins. I was also told by my dive master that they can only make one a night, so make sure not to shine the flashlight directly at them or disturb them if you ever see one!
Parrotfish make these snotty sleeping bags for many reasons. Some of the main pros of this transparent slimy sack are masking their scent from predators, an early alert system if anything comes too close for comfort, and most interestingly, for protection from parasites. Parasites such as the gnathiid isopod larvae latch onto the body of the fish and feed on their blood. With this cocoon, it becomes incredibly hard for these isopods to detect a scent or even get close to the fish. The queen parrotfish usually gets a spa treatment from cleaner wrasse during the day, making this nighttime behavior a fascinating evolutionary adaptation.
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