Aquarium & Tropical Fish Site

The Basics of Fish Nutrition

 Age of Aquariums > Aquarium Articles


Anybody who has been to a local fish store will have seen the shelves for fish food. So many brands! So many types! What should I get to ensure I'm fulfilling the nutritional requirements of my fish? Should I get color enhancing? Growth formula? What does it all mean? The purpose of my article is to hopefully answer some of these questions about fish food.

On the back of a package of flakes or pellets, there will be an ingredients list. On these lists, the further up an ingredient is on the list, the more of that ingredient there is in the food. Learning to read the ingredients list is important when it comes to choosing which brand you want. Good quality prepared food will derive their nutrients from an easily digestible source. Pretty high up on the list should be fish meal, shrimp meal or, for herbivore flakes, spirulina meal. If there is corn, rice, or cereal ingredients high on the list, that's not a good thing since they contain carbohydrates which fish have trouble digesting. They are okay if they are low on the ingredients list since that means they are probably being used as binders to hold the food together.

Probably the most important thing is to learn to understand the nutritional needs of your fish. The nutritional needs of each species depends on many factors and it's impossible to come up with a "1 size fits all" answer to their nutritional needs. Instead, I will go over the factors affecting nutritional needs so you can make your own decisions on how much of each nutrient is needed in your case. Here is a list of nutrients commonly listed on fish foods, as well as the factors affecting how much of each nutrient is needed. There are also micronutrients like Vitamin B and Vitamin C, but since they aren't usually listed on food containers, I won't mention them here.

Flake Foods Protein
Protein is, essentially, the building blocks of life. The amount of protein a fish needs depends on several factors. First of all, what the fish normally eats. Herbivores need about 25-40% protein in their diet, while carnivores need 40-50%. The age of the fish is another factor. If a fish is fully grown, then it needs less protein than a young growing fish or fry. Fully grown fish needs are in the lower end of what is recommended for them, depending on whether they are carnivores or herbivores. Finally, breeding fish need higher amounts of protein, especially females since producing eggs takes a lot of protein. Males need more protein to help them grow flashy fins and colors needed for displaying and courtship. Males won't need as much protein as females during breeding.

Fiber is used by fish to help them digest their food. Carnivores don't need as much fiber as herbivores (since it's easier for them to digest meat) and they need less than 4%. Herbivores, on the other hand, need higher amounts, about 5-10% because plant matter is more difficult to digest.

Fish diets should be low in fat since fat has the same effect on fish as it does for us. Useful in small amounts, but it's just plain unhealthy to comsume too much fat. As with fiber, the main factor is whether the fish is a herbivore or a carnivore. Herbivores need 3% or less, and carnivores need no more than 8%. Another thing to consider is the age of fish. Growing fish also need more fat than fully grown fish.

Not really a nutrient, but I will mention it since it is listed on most foods. Buying foods high in moisture is not a good thing since the moisture is just a filler and your fish have all the water they need (or at least they should).

This is definitely something that should be as low as possible, especially for people with reef tanks. Phosphorous is a nutrient, but not one for fish. It's for algae, and excess phosphorous from uneaten fish food will fuel algae growth in the aquarium. Good quality flake foods will have very low percentages of phosphorous.

Types of food
This is an overview of the types of prepared foods commonly sold at fish and pet stores. By prepared food, I mean food that has been processed and put into a canister, so I will not be looking at live foods.

  • Flakes: Probably the most common type of food sold for fish, this is just a blend of food ingredients that was dried into flake form. Flakes make a great staple diet for your fish and are best for small to medium sized fish. Good quality brands usually have balanced nutrition.
  • Pellets: The same principle of flakes, but formed into pellets. These foods are for larger fish since they are more filling than thin little flakes. Most cichlid food is in pellet form, although some manufacturers make micro-pellets for small fish.
  • Frozen foods: these are usually natural ingredients, such as brine shrimp or mysid shrimp packed together in little cubes and frozen. These foods need to be refrigerated, obviously. They are more expensive and are usually used as treats or to condition breeding fishes. When buying frozen foods, buy packages 250 grams or larger since the smaller packages will melt by the time they get home and re-freezing foods is not a good thing since it tends to lose nutritious value.
  • Freeze-dried foods: These are the least processed of all the prepared foods. They're basically live ingredients freeze-dried and packaged. These foods have less nutrition loss than frozen foods. They also keep for a long time and don't have the risks of disease or parasites that live foods have.
  • Sinking wafers: The most common type of food offered for bottom feeders, this is usually algae or other ingredients packed into a thin disk that sinks to the bottom. They are usually algae wafers for plecos or algae eating catfish, although there are also meatier wafers for cories and loaches.

Types of Flakes
In the Introduction, I listed several types of flakes. Here, I will go over some specialized types in more detail.

  • Herbivore flakes: These are flakes with more algae and plant matter for herbivorous fish. When buying these foods, check that spirulina meal is high on the ingredients list. Many brands actually contain more fish meal than spirulina meal in food for herbivores!
  • Growth formula: These foods contain more protein, which lets fish grow faster. For obvious reasons, these flakes are not meant for fully grown fish.
  • Color enhancing flakes: These are very common type of flakes. They enhance the yellow/orange/red colors in fish due to the addition of Beta-Carotene and other ingredients. Check the list and make sure that there are lots of shrimp type ingredients, since shrimp contain the pigments that enhances these colors.

Finally, one thing about fish food that you may have heard around is that flakes lose their nutrition over time. Some people toss out their food after only a month or two, because they think it's already too vitamin deficient. How long should you really wait? After about 4 months, the vitamins (but not the protein) start to deteriorate. You could go about 6 months without losing too many vitamins, but if you're keeping cans of food for a year or longer, you should consider buying smaller containers. Keeping food in the fridge will prolong shelf life for over a year.

Also keep in mind that variety is important. Try alternating various brands and types of foods for your fish. Just like us, fish can get pretty bored of eating the same thing every single day. It's also important to alternate because of several micronutrients that may be unavailable with one food type but available in another.

In summary, in this article I have tried to present a basic look into fish nutrition, but the topic of course much more complex, to the point that there is still a great deal of academic research being conducted on the subject. While what is written here barely touches the surface of fish nutrition, I hope that by supplying the basics, I can help you make a more educated decision when buying food for your fish.

Reader Comments Comment

May I add that vegetables are also good foods. Some veggies are important to herbivorious fish, usually plecos such as the bristlenose catfish. But it should be removed after a day because it starts to release small amounts of ammonia and such. Some veggies to use are zucchini, cucumber, carrot (should be blanched), broccoli and sometimes sweet potatoes.

Contributed by DJ

 Submit a Comment 

Got some experience to share for this page? No registration necessary to contribute! Your privacy is respected: your e-mail is published only if you wish so. All submissions are reviewed before addition. Write based on your personal experiences, with no abbreviations, no chat lingo, and using proper punctuation and capitalization. Ready? Then send your comments!

oF <=> oC in <=> cm G <=> L