Upside down fish

[northern sole]

Tried to find answer elsewhere on internet but to no avail, I dive regularly on the Zenobia and always under the starboard funnel the fish are upside down, if you watch closely as the fish approach the funnel you will see them start to turn 180 degrees and as they pass under it they are on their side before turning all the way over, anyone got an answer why,

 

[tlt]

showing off!!

 

[Damselfish]

I've seen some fish do that under ledges on reefs, they just swim around as if whatever nearby surface is the "bottom." My guess would be the hard surface provides protection in that direction and they can keep an eye out for predators better this way. Pure speculation on my part though.

 

[Puffer Fish]

There are are a fair number of fish that swim with the hard surface under them.. which means upside down to us when under a ledge.. this guy, for example:

Note: I turned the picture upside down, so it would look normal.

 

[Belmont]

I regularly see bass and other species swim sideways along a granite wall in the St-Lawrence river

 

[northern sole]

Thanks for all the imput guys but surely there must be a scientific explanation why this happens, I will keep looking for the answer though as divers ask me why this happens and i struggle to give them an answer,

 

[fire_diver]

Others already gave the answer. It's a defense mechanism. They keep thier bellies to the hard surface so they can keep a better watch for predators.

 

[DA Aquamaster]

Yes, it's not rocket science. They have a better field of view in the "up" direction and will invert to ensure their bellies are next to the hard surface to ensure they are defended and not going to be able to have predators sneak up in the areas where they have no field of vision.

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I have seen catfish sleeping way back in caves in an inverted positon (gotta dive the weekdays in the less traveled passages) when they wake up, they go right side up again. I suspect it is because it does not really matter what side is up in the dark, but when the see your lights, they adjust to the proper orientation over the silty bottom of the cave - again most likely for defense and field of view issues.