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Saturday, 18 August 2012

Do fish sleep?

A common question I've been asked over my years of keeping fish, do they sleep?

Well every living thing “sleeps” to some degree. However as human beings go, we are a typically jaded to the fact that sleep involves shutting your eyes and finding somewhere warm and comfortable and then off to dream land.

Most mammals, birds and reptiles, in fact, most none aquatic based beings follow a similar pattern, amply demonstrated by my cat Millie, the dominant and most experiences species when it comes to the art of catching 40 winks!

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So how do you sleep when you don't have eye lids and the potential to be swept away by water currents… or sink?

I have always enjoyed looking into my aquariums in the small hours of the mornings as much as i do when they lights are on. Many nocturnal species can be very interesting to watch during these quieter times, especially in marine/reef setups where many of the invertebrates will be active and some select fish species.

The fish then, that spend most of their time out in the open, this is their time to recuperate, and i have noted many examples of how they go about it.

In all cases, fish “shut down” into that state that we are all familiar with. But remember we do not go completely motionless. We continue to breath etc.. and most people will make the odd autonomous movements to regain comfort or when the body senses the blood supply being cut off.

Angel Fish are a good species to observe at night, i used to keep a magnificent breeding pair of wild caught Angles several years ago and they would remain in the main body of the water, yet they would appear to be in a state of suspended animation.

They would hang floating in the water, not moving a millimetre against the flow of water. Their fins would be slowly moving in a circular motion, keeping themselves stable and upright. Their gills would continue to open and close gently, as would their mouth, and their eyes would be just completely transfixed, staring off into the distance.

As long as you were slow and didn't make any sudden movements you could sit their and watch them. If you did make a startling movement or somehow significantly changed the light activity, they would suddenly “wake” and bolt to the other side of the tank.

Very similar to if you jumped on somebodies be while they're sleeping, or crept about and not disturbing them.

The Dwarf Gourami's that i keep at the moment, have a similar ritual, however they appear to find a nook or small cave to sleep in. They appear to prefer a bit of security rather than the Angels which had the speed and performance to outwit predators should it be looming upon them.

I find the Gourami's to sit in plants, shuffle up against bits of wood or rocks, or get inside ornaments. One of mine in particular likes to sleep in the sunken tank ornament!

And finally, there are the fish that seem to literally sink to a stop and literally lie on whatever surface they find or favour. The Dwarf Puffers are especially prone to this.

I have managed to capture a few images of them doing such things, sorry, some are blurred as i had to do my best to take the images with a remote light source as to not scare them.

One Puffer beds down right in the corner of the tank on the sand bed…

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Another on the sand bed out in the middle…

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Sometimes a leaf makes as a comfy hammock type arrangement…

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Or get in between two leaves of a plant…

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Finally you could always kept comfy on the ornaments!

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So do they sleep? Well yes, both scientifically and physically as far as i am concerned, and its another great way to observe your aquariums live stock, should you want to be up early in the morning!

Working shifts as i do is always an advantage and i tend to eat my breakfast sat in front of the aquarium watching them all sleep… wishing i was still doing the same!

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