# Can fish see blue light.



## Donald Hansen

Can fish see blue light? I know from this site that marine tanks with live coral need blue light to be healthy. Some where on this site I thought I read that fish can't see blue light. I did some searching but can't find an answer either way.

The reason for my question. It would be nice to watch my common pleco who 95% of the time only comes out at night and see if he's eating the Spinach and Zucchini I put in the tank at lights out. 


DLH


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## holly12

Not sure about blue..... but I saw a show "Blue Planet" where deep near the bottom of the ocean, some predator fish use a red light to illuminate the water around them, to find their prey (who can't see the red light).

I found this: What are reef aquarium lights for? - Yahoo! Answers Down in the response the person gives the reason why salt water tanks use blue light, and FW usually don't, (doesn't look as natural), but also says it shouldn't hurt anything.

If you try it and find that your pleco or other fish seem stressed, just turn it off and stop using it.


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## Donald Hansen

Thanks. That about doubled what I did know about the blue lights. I'm beginning to think it was my imagination because if it was true, that fish can't see blue light, it would be mentioned.

DLH


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## majerah1

They can see red.I have a cat pointer,and the fish chase it too,lol.Not sure on the blue though.


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## holly12

Nono, I meant the deep ocean fish. It was an educational show on the Blue Planet series. Apparently those fish can't see the red light.


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## Lil Gashog

holly12 said:


> Nono, I meant the deep ocean fish. It was an educational show on the Blue Planet series. Apparently those fish can't see the red light.


Its so dark,I think most of them are blind anyway


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## holly12

Probably. But that predator fish can see the prey in the red light.... shadows maybe?


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## ReStart

Below about 90 feet, only blue light, Indigo and Violet will penetrate. I can be looking at a piece of coral at 130 that looks only blue/purple and then shine a light on it and it now is bright red and white. 

The deep water collum absorbs light colors execpt BIV, you remember, ROYGBIV in the spectrum? Red disappears somewhere around 40-60 feet. When I got eel bit, the artieral blood squrting out looked like coffee. I don't remember exactly how deep I was but the bottom was at 50 as I recall.

So yeah, 100% true, fish can see blue light. When a shark swims out to you at 120 feet, he/she is damn sure looking at you. I promise.

At about 600-800 feet only dim violet is visible and those deep fish can see.


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## jrman83

Fish don't need to see their prey...they use their lateral line for most things anyway.

DLH, have you tried some moonlight type lights when your regular light goes out to see if you can watch your pleco then? Maybe worth a shot. I believe you can find fairly cheap LED kits that offer red, green, and blue. Somebody on here has them.


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## Donald Hansen

I haven't tried any blue lights yet, but I was thinking about maybe I would try and borrow one. If it worked then I would think about buying one, the lfs has one about a foot long and with maybe 12 LEDs for $40, or better yet since I made my living as an electronics tech, I could build one. I know I could beat the $40 price but I doubt my case would be as pretty.

DLH


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## beaslbob

I really don't know but feel it would vary is the species. Afterall cave fish are blind.

As I remember the most common form of color blindness is red/green because the rods or cones in the retnia are missing. Which is true for dogs. (can't teach them red or green traffic lights for instance--they have to look at traffic.)

But that's just my speculation.

Based upon no knowledge or experience.

Therefore worth even less than



.02


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## Donald Hansen

I'm *somewhat* color blind in reds/greens. Can't ever pass that test. Yes, I can see red and green stop lights.

I have an idea about a case if I do decide on getting blue lights. I looked and sure enough there's plenty of room inside my existing light fixtures to mount any number of LEDs. That problem is solved.

DLH


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## jrman83

Ask hydromatic where he got his LED setup. Don't think he paid that much.


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## holly12

I'm not crazy! It was on "Blue Plantet" and "Planet Earth". Lol. Red light.... lit up the surroundings so the fish could see his prey. I've got the D.V.D. Unless Discovery lied to us all!!! Lol!


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