What Is A Carotenoid?
A carotenoid is a class of fat-soluble pigments (meaning the pigments dissolve in or with fat and can’t be dissolved or degraded by water.) They’re mainly thought of as yellow, orange, or red colors and occur naturally such as in autumn leaves, carrots, or red peppers. There are several different “types” of carotenoids and it’s useful to know what they are and what they do if you want to bring out the coloration in your fish.
Most commonly, in aquarium keeping, we use knowledge of carotenoids to enhance fish colors by either adding them to fish food, looking for fish food containing the pigments, or by making fish food. These pigments are used differently by different fish, each pigment can be utilized as-is, deposited for enhancing another color, or can be converted to another carotenoid.
For example, β-carotene is probably the most widely known carotenoid, it’s what gives carrots their orange coloration. Daphnia convert γ-carotene to β-carotene. Many blue fish can use β-carotene to enhance their blue coloration, and many orange fish can use β-carotene as is to enhance their orange.
In humans, carotenoids act as an antioxidant and it seems like fish can utilize them the same way as well. Interestingly, it seems like fish also need carotenoids in order to develop muscles and retain muscle function. Some fish also appear to need cartenoids to be better parents – weird, but that’s what studies indicate. It’s incredibly useful to learn about carotenoids if you plan on breeding and selling fish as well, since they go a long way in making your fish more appealing.
However, it’s important to note that once you stop feeding carotenoids, the color will fade relatively quickly (depending on the levels you were feeding and for how long) it may be as short as a week.
Examples of Carotenoids
There are a plethora of carotenoids, and this is by no means a definitive list. When adding them to fish foods, rest assured they’re not water-soluble and won’t be dissolved or degraded when exposed to moisture. I did try to include all the pertinent ones here I could think of as well as their corresponding source should you want to add it your your fish’s food:
β-carotene (Beta carotene):
Beta carotene is the most commonly known pigment and it produces orange. It’s commonly available in multivitamins because humans can convert it to vitamin A (which is usually what the “Vitamin A” on the label is derrived from.) Many people use crushed multivitamins in fish food with no ill effect.
y-carotene (Gamma carotene):
Gamma carotene produces yellows and is often found alongside beta carotene in multivitamins (vitamin a.).
Lutein:
Lutein is a greenish-yellowish pigment common in most yellow plants as well as dark leafy green vegetables (such as kale.) You can buy lutein supplements derived from marigold leaves, and most contain Zeaxanthin as well.
I’ve heard some people cracking open the soft gels and pouring them into the food they’re making, but I’ve never tried this.
Zeaxanthin:
Is responsible for a wide variety of colors ranging from deep reds to oranges to yellows. It’s commonly found in paprika which is widely used in fish foods as a source of carotenoids. Although I’ve never met a fish that liked paprika in their fish food, some other fish keepers have reported success on this front.
Astaxanthin:
Astaxanthin produces a red carotenoid, and you can buy it in a powder form from some select suppliers. The fish-grade version is much cheaper than the human-grade version of the supplement and there’s not much of a difference, that I’ve noticed, between feeding the two. This carotenoid is helpful for bringing out red-oranges or deeper oranges in orange fish and certainly goes a long way in enhancing red coloration.
Spirulina:
Complex carotenoid mix. Though exactly what they all are, I’m unsure. It’s been noted fish fed spirulina show enhancements in the red, orange, blue, and green coloration – the most impact in that order. Enhancing the green and blue colors of any fish are difficult and this algae proves to be the most helpful in that case.
Further reading & Sources
Nature – Antioxidants can change fish behavior
NCBI – Carotenoid-Based Coloration In Cichlids
Semantics Scholar – Use of natural carotenoid pigmentation in fish