I think (I hope!) that any food coloring you can buy in a store is nontoxic for humans. This probably means it is also nontoxic for fish, although you never know -- that's why it's good to do experiments. But I suspect that simply putting fish in dyed water probably won't hurt them too much. However, many fish rely on vision to find their food, so if the water is so heavily dyed that they can't see very well, then they might have trouble catching prey and won't grow very much. They might even starve to death, if you ran the experiment long enough. To see this effect you'd probably have to feed fish live food, like brine shrimp, instead of just using fish flakes. If you're planning to buy your fish from a pet store, I would explain your project to someone who works there -- he or she might have some good ideas about what kind of fish and food would be best to use.Good luck with your project!

This is a great idea for a topic.I would not use food coloring, mainly because you can accomplish a similar objective without it. Food coloring is generally harmless, but it may be toxic to fish...you never know.

What you must consider is what you mean by "color of the water". Water (H₂O) does not have much color because it does not reflect light very well. When the ocean looks blue, it is actually just that it absorbs almost all of the other colors completely, and reflects a tiny bit of blue back at your eyes. This is why deep water looks blue and a cup of water looks clear.

When you put food coloring in water, you are adding material which reflects a certain color of light (a certain wavelength) very well, but also absorbs other colors. For the fish, you are mainly changing the AMOUNT of light which reaches the fish, and then secondarily changing which colors reach it.

A better option would be to find translucent plastic in different colors to wrap the fish tank in or to put over the lights shining on the different tanks. You can also get different colored bulbs at pet stores. These plastics will selectively allow different wavelengths of light to pass through while blocking the rest, so that the light you see has many components completely removed and looks a single color. This way the fish is getting just one main color of light. You can use colored plastic wrap (Available at grocery stores) or get plastics of different colors at a hobby store or craft store. Remember, they have to be thin and see-through.

Good luck!

If you're using food coloring intended for human consumption, and don't use more than a couple of drops, they'll probably be fine. My question for you is what will this tell you about fish? When scientists do an experiment, they generally have a question or guess (hypothesis) that they are trying to investigate. Why do you think water color will influence lifespan?

I know you will be taking good care of your fish. They will probably all still be alive at the end of your experiment, which is a good thing. However, if you are looking at how color influences their lifespan, you probably won't have an answer.

I suggest studying something about your fish that will give you guaranteed data right away. For example, do they find one color food faster than another color? That will tell you something about fish vision and hunting. Do they find food faster if the color of the food is the same as the color of the water? You would still be changing water color, but could gather data every day and also learn about fish vision. If you provide them with gravel or backgrounds of two different colors, where do they spend more time? That will tell you about the habitat preferences of fish and whether they prefer one color over another. You could also do that experiment using lights of two different colors shining on two different ends of the tank, but you would have to monitor the temperature.

Can you think of other questions that you will be able to answer between now and when you have to prepare your presentation or paper? Feel free to ask more questions when you have more ideas.

Thanks for asking,

The short answer to your question is: not unless the dye is toxic to the fish. Some dyes are thought to be toxic, especially the ones used in fabrics. The dyes used in food coloring shouldn't be toxic to humans, because we eat them. This doesn't necessarily mean that they are not toxic to fish. A better question for your science experiment might be: are food coloring dyes toxic to fish? If so, which colors, and at what concentrations?

As long as the water is the same in every other sense (same oxygen content, same food content, same pH, same concentration of salts, same temperature, same fish tank, etc.), then the color of the water shouldn't make a difference if the dyes are not toxic. However, this is kind of an interesting question, because in the ocean, what changes the color of ocean water is the stuff in it, and this stuff can affect food content, oxygen content and pH, so the natural color of ocean water does have some effect on the fish that live in it. I'll tell you why.

Pure, crystal clear ocean water is blue.

When you add mud and dirt, the water turns a yellow/tan/brown color. This dirt can clog fish gills, which cause the gills to not work as well, which can slowly suffocate the fish. Usually, the dirt and mud gets washed in from rivers, and the stuff that gets washed in with it can cause bacteria to grow. Since bacteria use oxygen, too much bacteria in the water can cut down on the amount of oxygen available to the fish and the fish don't do well. Also, the dirt and mud shade the water, so plants can't get enough sunlight, which reduces food and oxygen, since plants make oxygen.

When you add a lot of algae, the water turns green. Some fish eat algae, and some fish eat things that eat algae, so this can increase their food, and their oxygen. This will increase the health of the fish. However, too much algae and the bacteria grow again, especially when the algae dies. (Bacteria feed off dead stuff.) The bacteria will eventually take up all the oxygen in the water, which will cause the fish to suffocate. This is why you have to clean your fish tank all the time.