[Coral-List] Why do fish swim upside down in caves?

Fri Feb 5 14:26:56 EST 2016

I remember talking to Mike Land on the RRS Discovery about some mesopelagic amphipods he had been looking at.  The assumption was that their bilobed eye was an adaption for the differences in light quality/quantity depending on whther you looked up or down.  The ventral portion of the eye was apparently adapted for dim environments while the dorsal was adapted for vertically downwelling light.  It all made perfect sense (and was seen for example in mesopelagic decapods).  However when he observed the animals in a tank he thought that they were  sometimes using the dorsal portion of their eye to scan (as we might with our fovea) and swam in all sorts of orientations.  Shaun Collin did lots of interesting work on the retinae of reef and deep sea teleosts and found that the foveal geography reflected their lifestyle.

So my guess would be that fish can swim upside-down as easily as the "right way" around and their eyes will be adapted to a particular orientation with respect to the "bottom" (as suggested below).  Whatever, "Ecovisiology" is very cool!

Collin S, Partridge J (1996) Fish Vision: Retinal specializations in the eyes of deep-sea teleosts. J Fish Biol 49:157–174.
Johnson M, Shelton P, Gaten E, Herring P (2000) Relationship of dorsoventral eyeshine distributions to habitat depth and animal size in mesopelagic decapods. Biol Bull 199:6–13.
Land MF (2009) Locomotion and visual behaviour of mid-Water crustaceans. J Mar Biol Assoc United Kingdom 72:41. doi: 10.1017/S0025315400048773

________________________________________
From: BRUCE CARLSON [exallias2 at gmail.com]
Sent: 04 February 2016 19:58
To: psammarco at lumcon.edu
Cc: Coral-List at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Why do fish swim upside down in caves?

I think of it this way:  if I’m lying on the floor, I have a very hard time eating if I’m on my back; roll over and it’s easy to eat.  OK, that’s not quite the same as this situation, but perhaps for the grouper there is a greater efficiency feeding if your ventral side stays oriented towards the substratum, especially if you’re a carnivore feeding on fish that might pop out of the holes.  I can’t quite imagine how they would feed efficiently with their back to the rock.   Other larger groupers that may not feed on little fish in holes would be better off just remaining in the “normal” orientation.

Just guessing.
Bruce

> On Feb 4, 2016, at 5:25 AM, Paul Sammarco <psammarco at lumcon.edu> wrote:
>
> Dear Charles,
>
> Hello.  This is all a guessing game, but my suspicion is that the phenomenon may be a combination of two things.  Firstly, where is direct or reflected light coming from?  Which way is it light, and which way is it dark?  Also, perhaps it's also a matter of looking dorsally for predators.  They should certainly know which way is up and which way is down.
>
> Food for thought.
>
> Cheers,
>
> Paul
>
> Paul W. Sammarco, Ph.D.
> Professor
> Louisiana Universities Marine Consortium (LUMCON)
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> -----Original Message-----
> From: coral-list-bounces at coral.aoml.noaa.gov [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Charles Delbeek
> Sent: Wednesday, February 03, 2016 3:22 PM
> To: Coral-List at coral.aoml.noaa.gov
> Subject: [Coral-List] Why do fish swim upside down in caves?
>
> Our exhibit design consultant asked me this question concerning Cephalopholis polleni.
>
> My thoughts were that since these fish are bottom oriented they feel more secure with something on their ventral surface, I also believe they can see more what is ahead and below them where most predators come from for bottom oriented fish?? Also when a fish swims into a cave or overhang they are swimming down a reef face and coming across the opening so it is safer to remain oriented to the rock face then twisting and turning as they enter to cave/crevice. Also the shelter holes are in the ceiling so it is easier to dart into them when it is below them then above their line of sight, but I am just guessing on these.
>
> Anyone have something more definitive on this?
>
> Thanks in advance!
>
> Best regards,
>
>
> *J. Charles Delbeek, M.Sc. *Assistant Curator, Steinhart Aquarium California Academy of Sciences
>
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BRUCE CARLSON
exallias2 at gmail.com
BCarlson at GeorgiaAquarium.org

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