Fish can see Red Light?

[SteveMM62Reef]

I got a Red LED Penlight, that was advertised for Night Vision, reading maps, checking for animals at night. It replaces my MiniMag with the Red Lens, that disappeared. Didn’t notice fish could see this light, new light is brighter with a narrower beam. Even backing off, it seems they see the light. I’m Using it for Invert checks at night.

 

[ISpeakForTheSeas]

Yeah, despite common belief to the contrary, only deep sea fish (200 meters deep and deeper) can't see red light - shallow/non-deepwater fish like we get in the hobby can see red light (and some can see UV and Infrared as well):

Pelagic organisms avoid white, blue, and red artificial light from scientific instruments - Scientific Reports

In situ observations of pelagic fish and zooplankton with optical instruments usually rely on external light sources. However, artificial light may attract or repulse marine organisms, which results in biased measurements. It is often assumed that most pelagic organisms do not perceive the red...

www.nature.com

-Some fish (like salmon) and inverts (like mantis shrimp) can see infrared.

Freshwater fish, amphibians supercharge their ability to see infrared light

Salmon and other freshwater fish and amphibians supercharge their ability to see red and infrared light. Scientists at the School of Medicine have shown that this evolutionary adaptation hinges on the activity of an enzyme that converts vitamin A1 to vitamin A2, enabling the aquatic creatures to...

source.wustl.edu

https://www.science.org/content/article/new-form-vision-discovered#:~:text=Mantis%20shrimp%20eyes%20can%20see,in%20mating%20or%20secret%20signaling&text=When%20it%20comes%20to%20versatile,its%20color%20vision%20tops%20ours.

That said, clownfish can also see UV light,** so it may be rather bright in there for the clown too (it may hurt the clown's eyes if it's bright enough). - Fun fact for anyone interested here, the UV reflectance of clownfish is also related to intraspecific aggression and their social hierarchy.***

**Source:

Molecular Evolution of Ultraviolet Visual Opsins and Spectral Tuning of Photoreceptors in Anemonefishes (Amphiprioninae) - PMC

Many animals including birds, reptiles, insects, and teleost fishes can see ultraviolet (UV) light (shorter than 400 nm), which has functional importance for foraging and communication. For coral reef fishes, shallow reef environments transmit a ...

www.ncbi.nlm.nih.gov

***Source:

Higher ultraviolet skin reflectance signals submissiveness in the anemonefish, Amphiprion akindynos

When signaling submission, it is important to wave the “white flag.” In the Barrier Reef anemonefish, ultraviolet color patterns serve to signal submissive

academic.oup.com

 

[i cant think]

Yeah, despite common belief to the contrary, only deep sea fish (200 meters deep and deeper) can't see red light - shallow/non-deepwater fish like we get in the hobby can see red light (and some can see UV and Infrared as well):

Pelagic organisms avoid white, blue, and red artificial light from scientific instruments - Scientific Reports

In situ observations of pelagic fish and zooplankton with optical instruments usually rely on external light sources. However, artificial light may attract or repulse marine organisms, which results in biased measurements. It is often assumed that most pelagic organisms do not perceive the red...

www.nature.com

Sometimes it’s scary knowing what fish can do, we tend to say they’re dumb and such but actually some of them are insanely clever.

 

[VintageReefer]

I do think they can see red light but have reduced vision. I had to catch some fish in my display and was failing miserably and searched the forums and people suggested using red light only.

I set my led to reds only on 5-10% (I forget) and I had both fish caught in a few minutes. They did see my net and acclimation box that I was herding them into, but when I tried with blues on 3-5% they were much more aware and completely avoided the box