Why does it.....?

michelle56 · Post by **michelle56** » 20 Dec 2003, 17:07

Look like my cory's fins looked ripped?
And why does it looks like my cory blinks?

clay · Post by **clay** » 21 Dec 2003, 03:39

they are "blinking" and what other fish do you have in the tank?

michelle56 · Post by **michelle56** » 21 Dec 2003, 03:45

clay wrote: what other fish do you have in the tank?

Blackskirt tetras, a Glass Fish, A Molly, Bigeye Shiners, I think thats it other than my 2 Spotted Cories.

Post by **Coryman** » 21 Dec 2003, 10:56

michelle56,

The ragged fins could very well be the result of what you call the 'Black scirt tetra's, We call them 'Merry widow's here in the UK, they do have a reputation of being nippers, I don't know how many you have but they are least trouble when kept in decent sized shoals (8 -10).

The blinkling is a natural Cory action, they are actually rolling their eyes, having a 360Âº look see. All species do it and it's quite commical to see.

Ian

YouTube · Post by **Jools** » 21 Dec 2003, 12:41

I actually spent two hours one day (some time ago now) filming my corys trying to get this onto video so I could use it as an avatar or the like. Never managed it, but it would be cool to have on record.

Jools

magnum4 · Post by **magnum4** » 21 Dec 2003, 17:53

a Glass Fish

another likely culprit.

michelle56 · Post by **michelle56** » 21 Dec 2003, 19:05

My Glass fish is to peaceful. And would of never thought of Blackshirts doing that.

Allan · Post by **Allan** » 23 Dec 2003, 23:25

I am quite sure that the Blinking-motion is to clean the eye. I have newer seen a cory blink in any other way than straight down and then back to normal position.

pleco_breeder · Post by **pleco_breeder** » 24 Dec 2003, 02:14

Hello,

Another possibility for the blinking motion would be for depth perception. I know that owls, I know we're talking about fish, don't have the ability to recognize how far an object is. That is the reason that they move their head in the circular motion. This gives them an idea from the objects movement. It would be possible that corys are simply trying to realize the distance of an object, or check for visible cues for food. I wouldn't think that a live tubifex would have much of a scent. A dead one on the other hand

It would conserve energy if they have the ability to see local food sources without an obvious scent. The other option would be to shove their heads in the sand for a mile of stream in hopes of finding a bed of tubifex. Evolution says that it makes sense.

Larry Vires

Allan · Post by **Allan** » 26 Dec 2003, 00:19

depth perception

I just think they blink way to fast for that, and still the eye of the cory stay'es in the same place under the blinking, i don't think a quick glanse towards the bottom will help depth perception.

Also, why do they turn all the iris down to a no-see position, if it was dept perception they were seeking?

Im still quite sure about this being their way of cleaning the eyes.

sass · Post by **sass** » 26 Dec 2003, 00:41

I would have to agree with Allan on this subject. The shutting of the eyes are in my oppinion to fast to be a depth perception, and the eyes never changes its direction.
To the owls, as I understand it, the hearing is more important to those birds. The ear is not placed at the same hight and depth on each side of the owls head, and there for it can determine the location of prey only by sound. The parabols around the eyes is for optimising hearing also. And another thing that makes the depth perception for owls strange to me, is that the owl has it eyes pointing forewards, so it has more double seight than a normal bird of prey has.
So my suggestion would be, that the corys blinks it eyes to clean it for sand and other stof when it is searching for food.
Best regards
Thomas

michelle56 · Post by **michelle56** » 26 Dec 2003, 02:33

kept in decent sized shoals (8 -10).

What!?!?!?! its a ten gallon tank!
I have 3 of them.

Post by **Coryman** » 26 Dec 2003, 13:33

Corys do not have eye lids so they cannot actually close their eyes so IMO the eye cleaning theory is not viable, I have watched this action many times and I still back my original theory of the rolling eye action to make a rapid all round observation of its suroundings. I do not have a video camera to film the action, but this would be the way to see the action and play it back in slow motion.

michelle56, Cory's are almost always kept in good sized groups.

Ian

Allan · Post by **Allan** » 27 Dec 2003, 02:22

Offcourse they dont have eyelids. If they had eyelids they would close them and not roll their eye.

Don't you agree, Coryman, that the eye moves just down and then up to normal?

Don't we have any trained biologists on board who can enlighten os on this subject?

JdubsVW · Post by **JdubsVW** » 30 Dec 2003, 18:09

when it comes to cories Ian is about as close to a "trained biologist" for cories you are going to find. And the fact that they do roll their eyes in the reason I actually bought some I didnt like them when I first got into the hobby then my ex-gf's parents bought a tank ( after someone kept bugging them

) and they bought some albino and I watched them and I was sold then and there when I first saw them roll there eyes and interact with one another in a schoal. As for the whole deal with purpose of eyerolling. the idea that makes the most sence as other fish dont need to "clean" there eyes. and the motion is too fast to try to focus on one single object for depth perception.

Allan · Post by **Allan** » 30 Dec 2003, 23:43

I have great respect for Ian and his breedingresults and great species knowledge. But i do still think, that a scientific backgrund is a great plus in analysing what the purpose of this blinking motion is.

JdubsVW, i would also like to hear your description of this blinking motion. Study your cories, and descripe how the eye moves. If you see the iris moving to a no-see position, don't you agree that this is irrationel for "looking around"?
You say the motion is to fast for depth perception. Agreed here. But then why is it not to fast for looking around?

As i see the motion, i also dont find other fish that makes a rapid down/up motion to "have a look around". That is to me as good an argument as your argument against the eye-cleaning theory, being a sole cory thing. If the fish moves its eye to look around, then why make it such a rapid movement?

Still, i am quite firmly convinced, that the iris moves straight down, straight back to normal. This clashes with looking around. Also i find on the net, that fish (with fixed eyes ie trout) have a vision field on 300 degrees. Fish eyes have lenses shaped to give them a very big viewing field. Moving the eye would not extend this field, as it is actually having a constant look around. Try looking trough a carera-lens that is "fish-eye", this name for lenses is not an accident

The cories live close to sand and in detritus, often burrying their head to the gills in the substrate. This to me could indicate that an eyecleaning could be more needed in this species than many others, so an evolutionary step.

JdubsVW · Post by **JdubsVW** » 31 Dec 2003, 00:18

ok i see where your coming from but wouldnt you think the sand would scratch the fishes eyes ? I have cories that are not in sand that do this , are you saying you think they do instinctively ? I m not sayng your wrong and I m just asking your opinion on this. I dont actually know why they do it but I just think that it might not be a good thing for the fish to rub the sand into their eyes. But this is just my opinion, please let me know what you think... this being said.

Justin

Allan · Post by **Allan** » 31 Dec 2003, 00:56

I am not to say if this is instinct or not, this being beyond my abilities to determine. But i am quite sure, that allthough you don't have sand, there will still be detritus present in your tank. Instinct is a good guess to me allthough.

To the scratching of the eye, guess not. I newer had permanent damage to my eye, allthough i many times had sand and dust in them and blinked. Guess the moist enviroment and the softness of the eye prevents this.

If they blink their eye, it could be possible, that they have some glands under the eye, that leaves a protective film/secretion over the eye, but this last note is completely guessing from my part!

Happy new years
Allan

Post by **Coryman** » 31 Dec 2003, 00:57

This is a picture of a young C. amapaensis caught right in the act of "Blinking" The surface of the eye never actually gets hidden, the whole eye doen't role like I first said, it more or less rocks down and back up.

Now if you look at a Cory from the front and make a note of the shape of the fish, its a little toward triangular , especially the snouted species, with the widest point being just above the pectoral spines. Now the position of the eyes are not on the sides but higher on the hesd about three quarters up and in the natural position it would be extremly difficult for the fish to see straight down even thought it may have 300Âº vision.

Looking at the picture the eye in its tilted down position the fishes vision is now vertical. I really don't think that the "blinking" is a cleaning action because the surface of the eye is not covered at any time.

At this stage I don't have any conclusions.

Now there's a subject for a pHD thesis if ever I saw one.

Ian

Allan · Post by **Allan** » 31 Dec 2003, 01:47

Are You absolute sure that the iris is newer covered, Coryman? Cause then my eye is fooling me when im watching the critters.

I will try go borough a video-camera, i think this, as You statet earlier, will be better proof. But i do fear that filming it is quite impossible.

Isn't seeing down a bit irrationel for a bottom-dweller? - I mean, they blink sitting at the bottom.

When you look at a cory from the front, you still see the eyes. They greatly curved lenses really helps to give a wide look around.

A fisheye looks somewhat like this:

This should give a fish this view:

Edit: Picture by R. Oleson, [url]http://rick_oleson.tripod.com/[/url] , with permission.

When i look at my cories from front, i think this should give them a quite good look at the bottom allready.

If you are right about the iris newer beeing covered, then i am really puzzled. Is there any other oppinions on what this blinking could mean then, is it a social behaviour?

I think anyone who reads this thread, should go look at their Corys, and state whether they see the iris moving all down or not.

JdubsVW · Post by **JdubsVW** » 31 Dec 2003, 02:32

another thing to consider too is that plecs also do this. my clown and red and black both do this action as well as many others i have had in the past. I dont know what this is for other than instinct or social behavior its kinda like that whole tree falling in the woods thing i guess?!?

sass · Post by **sass** » 31 Dec 2003, 05:07

Hi again.

I follow this discussion with interest. I've been creating aquariumshots my self, and I found this picture of a C. haraldschultzi (not hte sharpest shot around, but shows what I mean).

IMO it shows that some of the pupil is covered by the skull, and I'm certain that the eye rolled all the way down, when I took the shot. To catch this motion on film (digital or analog) is a rather difficult task IMO, because the equitment should be pretty good, and the photographer needs quite a fast triggerfinger. So to get a shot where the eye is totally shut is a lucky shot (especially if the camera is a point and shot digital).
I would say, that some of the pupil is covered in this shot, which IMO must mean, that corys "close their eyes" in a movement that rolls the eye down and up again. IMO this means, as Allan and I have been saying the whole time, that the movement is a "down and up"-movement. As I see it, the movement is to fast for the fish to focus on anything, so IMO the most viable theory is cleaning of the eye.

Best regards

Thomas

pleco_breeder · Post by **pleco_breeder** » 31 Dec 2003, 06:49

Hello,

It would only make sense that if the eye were being cleaned there would be, at the minimum, a membrane which would have to wipe the eye. Neither of the pics submitted show any evidence for that argument.

However, if you look at the fisheye photo, if the lens were rolled down similar to the eye, the widest portion of the viewing range would no longer be on the horizon, but on the ground paralell with the fishes body. I am still sticking with the idea that they are trying to see something at their side. The most obvious of guesses would be a food source.

Larry Vires

sass · Post by **sass** » 31 Dec 2003, 12:46

Hi Plecobreeder.

I don't see why the corys would need a membrane to clean the eye. The motion is to fast for the fish to focus on a target on the ground. And what should it be looking for there in the first place. The enemies of the fish would attack either from a horizontal level or from above. If it's to see food, it does this motion, then IMO it would already be seen with the eye, because big angle of vision and the cory would, as I've been told, taste the food with its barbels, so why should it look down under it self in such a fast motion. I don't belive that the corys has a fixed focus on the eyes, so somehow, the lens that is placed behind the iris, has to be adjusted to se something this close. Just think of your own vision, or a cameras, when you are looking at something 5 inch in front of you and the you have to see something 200 yards away. It takes a moment for you eye to focus, and IMO it must be so with the fish to. Also, the shape of the head is triangular pointing upwards, so the vision wouldn't be double and the fish wouldn't be able to "measure" distance. What the motion should be fore, exept cleaning the eye from particles, or as Ian suggests, is a socail sign, I have difficulty to see.

Best regards
Thomas

pleco_breeder · Post by **pleco_breeder** » 31 Dec 2003, 18:46

Hello

The corys are blinking no where near as fast as a human blink, and we still have to have the membrane. Otherwise, they would nearly have to vibrate the eye in order for the water to clean it. I can see how it would apply to possible social interaction, but I've had single corys in a tank which still do this. In order to to say if it is looking at something, the neural response time comes into question. I don't have those times for fish, but in humans it is quite slow compared to other mammals. We just don't depend on our eyes as much as most species. Predatory animals normally have exceptional response times because of the search for food items. I'm still going to have to stick by my theory.

Larry Vires

JdubsVW · Post by **JdubsVW** » 31 Dec 2003, 20:21

i just thought of something else loaches also do this with their eyes I have 3 creek loaches that do this as well as a orange tail botia that does this. I dont know i m confused about all this as its something that we may never know the true answer to. I guess everyones theory has some sort of possibility

corydorus · Post by **corydorus** » 01 Jan 2004, 16:48

Will this help ?

Post by **Coryman** » 01 Jan 2004, 19:47

Thanks Denis, your picture shows the same action as I described where the eye surface is never actually covered which to me dispences with the cleaning idea.

As Larry said that if the fish eye lens is tilted down the horizon also lowers, true. So the fishes eye doing the same would position the maximum range of vision at a piont central to the eye and parallel to the substrate. The majority of preditors come from above (Birds) but Corys do have a few aquatic enemies, no where as many as birds but a Cory still needs to be alert to those dangers so being able to maximise vision would be a distinct advantage.

Ian

Allan · Post by **Allan** » 01 Jan 2004, 20:17

Hmmmm, who says that the eye is fotographed in the lowest position?

Corydorus, do you think your blink-pic is taken when the eye was at absolute lowest position?

So the fishes eye doing the same would position the maximum range of vision at a piont central to the eye and parallel to the substrate.

With tilting the eye it does not get a look parellel to the substrate, but into the substrate. In normal position, the central of the viewing field is parralel to the substrate. Not that a non-predatory fish has much defined central viewing field in the first place to my knowledge.

Everyone i show this motion to says that they guess on eye cleaning, to me this debate is really confusing. I'm amazed that noone has some durable documentation for either one or the other theori.

Don't someone like Silurus have an idea about this? - If he argues clearly against the eye cleaning theory, i will back down.

Post by **Coryman** » 02 Jan 2004, 00:23

A little bit more info, I have just spent some time watching and trying tp film the Cory blinking eye action and did manage to get a result how I can post it hear I do not know. It was done using my Fugi Finepix 602Z in video mode, which gives me about 30 seconds of movie. It is not in that good focus but good enough to see the action and the extreme amount of movement that the eye covers, which is no more than the three photo's show. The eye does not have the surface covered at any time. The eye tilts down by about 25Âº. I watched several fish for ten minutes or more and they also have limited forward and backward movement, but when looking down the eye was always in the central position.

I am totaly convinced that the action is for visual purposes and not a cleaning action.

Ian