Beautiful eyes

McEve · Post by **McEve** » Mon May 16, 2005 7:27 pm

Our Zebras do have beautiful eyes don't they

I'm still looking into what they can and cannot see, and came across this article in my never ending search for answers.

Interestingly, it turns out the pupil is in fact round, is mobile, and has an extra flap that covers the pupil, causing the V, or U, shape of the pupil that we always see in pictures and when watching them, and this flap is not only there to manage the amount of light that enters the eye - but is also a part of a camouflage technique.

But - the picture taken of the pupil, dilated and constricted (showing a bit down on the page, shortcut to it here) is taken with in IR camera, which makes me wonder if they can see IR after all... shouldn't the pupil be constricted if illuminated by light visible to the fish?

The previous documentation of IR-light being visible to the fish never stated catfish explicitly, merely stated that IR can be seen by most fish, and then judging by the way my male reacted I concluded that Zebra was one that could see IR.

This makes me wonder if it might have been the heat from the light he reacted to, instead of the light itself?

The language in the article is very heavy, at least for me

I couldn't find if they stated anywhere, explicitly or implicitly if they see IR?

Enough rambling on, would you care to have a look for me and see if this article says they can see IR or not?

Rob · Post by **Rob** » Mon May 16, 2005 7:48 pm

Wow thats amazing. Got to say McEve, have you ever though of follwing in the footsteps of "Magnum PI" (yes I realise this is a target audience......but I'm sure you have all heard of the man).

I've had a quick skim through, and I get what you're thinking, and yes it does make perfect sense. The idea behind using IR would be to not disturb the pupil.

I'll read on a bit. A possible comparison would be to find a similar picture of a pupil from an animal that DOES react to IR. That way we would know whether or not a reaction should be expected.

Looks like I'm stopping work for the night!!!

Rob

sparkee · Post by **sparkee** » Mon May 16, 2005 9:34 pm

i watch mine at night using a wireless ir cam, they dont seem to notice it at all.
if fact they are very frisky and so active, they are always jumping of bogwood, there caves and they chase each other like little kids in the playground.

McEve · Post by **McEve** » Mon May 16, 2005 9:41 pm

Hi Sparkee

I had one set up in the top corner of the tank for a while, and they didn't pay attention to that one at all. It wasn't until I put the cam in front of the males cave he panicked.... he settled down immediately when I turned it off, so there's no doubt it was the light, or the heat, he responded to, and not the camera itself.

Probably something similar to them not paying attention to the light in the hood, but don't like it when you shine a torch in to the cave I guess

It was a very violent reaction too

I still feel guilty about the whole thing, that's why I keep investigating what happened I guess.

sparkee · Post by **sparkee** » Mon May 16, 2005 9:51 pm

i have mine at an angel of about 45 degrees to the tank, right infront of there caves. when there lights go off i can see 6 twinkly lights moving about, getting closer to the food. and then feeding.
the cam i use is fitted with 10 ir led's and produces little heat.

McEve · Post by **McEve** » Mon May 16, 2005 9:55 pm

inside our ouside the tank? Oh - you indicate it's outside the cave

Mine was inside the tank. But everything is fine with the way you have it set up anyway, as they don't care about it

sparkee · Post by **sparkee** » Mon May 16, 2005 9:56 pm

outside about a foot away. if its not angeled it reflects the ir

McEve · Post by **McEve** » Mon May 16, 2005 10:01 pm

sorry about that - I edited the previous post when I realized

At that distance they wouldn't feel any heat, and wouldn't worry about normal light either. I set mine up about 15cm away from the cave entrance, inside the tank.

Mind you, I don't say it's the heat he reacted to! I'm still investigating what happened, and was sure up to now that it was because he saw the light. Maybe it wasn't, maybe it was, what I do know is that there's something he reacted to more than they do with "normal" light.

McEve · Post by **McEve** » Tue May 17, 2005 12:09 am

ok, this is getting complicated

I decided to do as Rob suggested, and find out if an animal known to se IR light will give a pupil response to IR light. In this quest I came across a page where a group of scientists has researched on blind mice for a few years - turns out their pupils respond to light, even though they're blind. So... pupil response doesn't nessesarily have to mean that you can or cannot see a light.....

Catfish has so many sensory organs all over their body, sensing vibrations, smell, heat, and whatnot, that it might be impossible to pinpoint what caused the reaction in my male.

At least that's how I feel now at 1AM

I think I'll call the university when the holiday is over and ask them what they know about pupils and IR - at least that question can, hopefully, be put to rest then.

valhallan · Post by **valhallan** » Tue May 17, 2005 4:11 am

Hi McEve,

If it would help, I'll speak to a friend of mine at work tomorrow. He runs the fish facility next to mine and his lab is involved in optics research. We both work with the zebra danio (danio rerio) but he might have some insight into your question.

Val

McEve · Post by **McEve** » Tue May 17, 2005 7:57 am

Hi valhallan,

Thank you, all input is much apreciated

McEve · Post by **McEve** » Tue May 24, 2005 8:54 pm

Further research suggests that they don't see the infrared light with the eyes, therefor the pupil will not contract when exposed to infrared light.

It is suggested that it is indeed the heat they respond to, and which they are able to form an image from. how that image looks like is not clear to me

Bottom line seems to be that the Zebra can see - or maybe only sense - infrared light, but with one of the multiple other sensory organs they have on their body. On a snake it's identified which organ it is, but I haven't found a reference to which organ on a catfish it is that act as reseptor for IR light....

Then again - maybe they only feel the heat from IR, and that's why my male reacted so violently to the cam when placed only 20cm from his cave. Maybe they don't have a sensory organ that converts the IR light to an image, but responds solely to the heat.

The search goes on

I find this topic facinating, I hope I don't bore the rest of you to tears!

valhallan · Post by **valhallan** » Thu May 26, 2005 9:30 pm

Hi McEve,

The guy I told you about hasn't been around the last couple of weeks, but I got chatting with someone else from his lab today and this is what he told me:

Fish actually can see infra red up to a wavelength of around 700nm, but that is the far end. Their red cones are more adjusted toward light wavelengths of around 600nm. He couldn't comment directly on catfish or loricariids, but this generally holds true for most fish. I quoted him some of the paper you were referring to and told him why I was asking the question. You were right in assuming that the researchers doing the experiment were using the IR camera for taking control pictures "in the absence of visible light", but it gets a little more comlicated than that. I can't remember off the top of my head if they actually stated the wavelength of the camera's IR output, but this is the key factor. If you use light of the correct wavelength, the fish won't be able to see it.

Hope this is of some use.

Val

McEve · Post by **McEve** » Thu May 26, 2005 10:37 pm

Thanks valhallan! That's very useful information, and also helps understanding infrared light a bit better, which is probably where I should have started in the first place. it never occured to me that IR has different wavelengths, even though it makes perfect sense!

Thanks for helping me a step closer to understanding, and thank you for taking the time too!

valhallan · Post by **valhallan** » Fri May 27, 2005 12:45 am

No problem. Glad I could help

Val