Four things tell me that
this fish is asleep:
- it’s normally a continuously swimming, midwater plankton feeder,
- it’s in its night time ‘pyjamas’ - a pink bottom half, with a grey and white stencil-striped top, together covering the normal silver and bright yellow stripes,
- it’s wedged itself into a corner between sand and reef, using extended dorsal and anal fins (see particularly how the normally vertical anal fin is bent laterally),
- it’s added an abducted, partly splayed pectoral fin as a lateral prop against the sand.
How commonly do animals sleep wedged in or propped up?
Do you have an accessible scientific resource which goes into more detail?
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An interesting topic. Just wanted to post a couple of projects somewhat related to your topic that may (or may not?) be of interest to you:
https://www.inaturalist.org/projects/sleepy-animals
https://www.inaturalist.org/projects/sleeping-animals-zzz
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Also this one: https://www.inaturalist.org/projects/sleepy-bee-slumber-parties
(revealing surprisingly similar sleeping strategies as that of the fish)
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It’s interesting to see how many of them use biting for stability. I don’t know if any fishes do this, although maybe Lampreys or Hagfishes can? Some, like Remoras, use suckers made from adapted fins.
I forgot I had previously downloaded a relevant 1996 article about primate postures, which notes (see this accessible pdf):
Foot-prop sit. Similar to sit-out, but the hindlimbs are flexed at the hips and extended at the knees, with the feet propped against a vertical support. The trunk may also flex at the hips, so that it rests against the hindlimbs. Common sleeping posture in its exemplar, Papio.
It would be interesting to get a link to an iNat observation example.
I know parrotfish in the Caribbean will secrete a mucus membrane around themselves as they sleep on the bottom of the reef overnight. The mucus balloon’s job is to control the spread of molecules that signal the fish is there so it’s less likely a nighttime predator will be able to find it.
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This paper on sleeping site selection in lizards: https://www.johnsonlizardlab.org/s/Singhaletal07.pdf
might be useful. The first author and I were graduate students in the same lab at Berkeley.
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Beautiful! Exactly what I’m looking for. It may explain why my high water column feeder doesn’t fully hide away in a crevice: maybe it keeps itself partly exposed to facilitate threat detection and reduce damage to itself if it attempts an escape darting motion in pitch darkness.
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Well, if you lack opposable thumbs, I guess you use whatever other bits of anatomy you have available to grasp things. Clamping onto plants with one’s mandibles when sleeping is not unique to bees – there are some other hymenopterans that are also sometimes seen doing this (e.g., gasteruptids and sphecids). With bees the practice is usually limited to males and possibly female cuckoo wasps, since females generally have a nest they can sleep in.
Most adult hymenopterans subsist mainly on nectar, so mandibles aren’t really used for eating; they’re more of a tool for grabbing, cutting, biting, and holding things: cutting nesting material, excavating holes, masticating prey, transporting prey (in the case of spider wasps, sometimes prey nearly as large as oneself), and so forth.
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