Fish out of water
February 13, 2017 11:56 PM   Subscribe

Can fish see through air? If you take a fish out of the water, can it resolve images and see as clearly as it presumably does in water? Or does its sight go all blurry the way mine does underwater?
posted by tavegyl to Science & Nature (3 answers total) 7 users marked this as a favorite
IANAFish but it should be blurry - you can't focus underwater because water doesn't have the right refractive index for your eye lens material. Presumably fish would have the opposite problem.
posted by Dr Dracator at 12:59 AM on February 14

If you take photos with a Nikonos lens (designed for Jacques Cousteau's underwater camera) in air there will be about 20% that is in focus.
posted by ridgerunner at 5:15 AM on February 14 [1 favorite]

This might be far beyond and in a direction that you want in an answer, OP, and if it is, please flag this. When I saw the generic word "fish" without specifying type of fish, environment, stage of development, then the answer for me falls into comparative anatomy and physiology for me and away we go.

Basically, it depends. What are the characteristics of the fish: What type of environment does the fish live in? Deep water vs. near the surface (i.e. amount of light), turbidity of water, where the fish might live as a juvenile vs. adult, and how much does the fish go to the surface and depend on its activities at the surface (as in, eyes partially out of the water or not?)

So if you are imagining a fish near that predominantly spends its life in a lake and near the bottom with a turbid environment, some of the answers in this thread already hit on the main concept. Light travels through in a straight line, but when it hits another medium (i.e. water, or a window), due to light refraction the path of light changes (this image shows the main idea, along with how various structures in a vertebrate eye can change the path of light - including the cornea and the lens); for an ideal image, light will travel through the lens and onto a point on the retina, which has photoreceptors that will detect light and sometimes color, transduce that information and send it onwards to the brain. The refractive index of water changes the pathway of light, so a fish already is optimized via the cornea and lens to fall on particular points of its retina. Air does not bend light (whereas water does), so the point of light is not going to be at the same point on the retina, and would be a distorted image for your generic fish that lives in deep water. Several types of fish have different type of photoreceptors depending on the environment they live in - so some can detect color, or see well in dim light, etc. (see some differences discussed in the discussion of this paper) - I'm bringing this up because the fish might not detect certain colors, or is optimized for dim light vs bright light, so there would be more differences than just blurry vs. not. tl;dr just based on the physics and different medium, your fish can see in air, but blurry.

But because we didn't specify type of fish and environment, this is where other types of fish come in. A type of fish that is often discussed/studied in comparative anatomy and physiology is the Anablep fish because it normally sits in water with half of its eye on the surface and in air, and the other half is immersed under water (see image of eye from a journal article). Anablep's daily living activities depend on clear vision both underwater and in the air. It's adapted to both environments by having changes to the cornea (top vs bottom, with thickness, for example, which will change how much light is refracted, there are many more differences listed in this journal article Adaptive differences in the structure andmacromolecular compositions of the air and watercorneas of the “four-eyed” fish (Anableps anableps)). Another big difference is that there are different sites on the retina for detecting objects from the air environment vs water environment. What's also intriguing if you want to continue to fall down the rabbit hole and go into molecular biology, there is also a difference in the type of gene expressions and proteins that make up the photoreceptors - there are some that are only in the retina for detecting images in the air, and there are some only in the retina for detecting aquatic images - see this image from this journal article In the four-eyed fish (Anableps anableps), the regions of the retina exposed to aquatic and aerial light do not express the same set of opsin genes). The question that would arise from this obviously is: What does this mean in terms of color detection and behavior, and per the authors in the paper, this is a question they will look into and will likely be part of a future publication. tl;dr Anablep fish will be able to see clearly out of the water, although only in part of their eye.

Anablep is not the only fish that does this. If you are really interested in looking at this more deeply, use key words like intertidal fish and vision in google scholar to additional journal articles and find out about other types of adaptations.

Good luck.
posted by Wolfster at 10:05 AM on February 14 [37 favorites]

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