FEEDING YOUR FISH
by Pearl A.
Fish need the right diet, like any pet. Malnourishment and vitamin deficiency cause stunted growth and weakness to diseases far more difficult to treat than prevent. Plus, for most people, the main attraction of keeping a fish tank is the vibrant colors and energy of their inhabitants – without a proper diet, you’re missing out.
Fish food comes in a wide range of formulas for different dietary needs and physical feeding habits. Many aquarium fish will not simply “adapt” to whatever kind of fish food you buy them. Plenty of hobbyists learn this the hard way!
Cichlid food is specialized for different cichlid species, including discus food and angelfish food. “Fry” food for baby fish, guppy food, tetra food, even crustacean food can be purchased. These are "staple" or daily diets, which should be supplemented with regular, natural treats. Betta fish food is a good staple, but bettas eat mosquito larvae in the wild, so occasional freeze-dried bloodworms keep them peppy!
Most freshwater fish food is for tropical fish – if you own goldfish or koi, look for goldfish food or pond fish food designed for cold water metabolisms. If you own fancy goldfish, buy fancy goldfish food – they have unique digestive tracts. The gastric system of any goldfish is prone to floating or digestive problems; some goldfish owners make their own foods to supplement commercial choices (more on this later).
If your fish doesn’t have its own tailor-made formula, don’t just grab a general “tropical” or “marine” fish food! Within a freshwater or saltwater tank, there can be big differences in dietary needs and feeding habits. Some quick research, online (here's a simple guide) or with reference books, will tell you a fish’s nutritional needs, as well as tips to encourage feeding!
Fish diets are specialized; they eat mainly (or only) plants, meats or both. This isn’t just a matter of taste – fish digestive systems are designed to process certain foods, and they simply can’t digest what they aren’t made to.
An ingredient list will place its primary components first; for carnivores, make sure that meat based proteins (from aquatic animals) come first, while herbivores should list vegetable based proteins like spirulina or soybean meal first, with no meats.
| Diet Type |
Restrictions |
Popular Example |
Natural Diet |
Staple Needs (Daily) |
Supplements (3x/week) |
| Carnivore |
Derive no/minimal nutrients from vegetation |
Bettas, Discus, Anthias |
Smaller fish, invertebrates, crustaceans, insects |
Fish-protein based (fish meals, squid meals, shrimp, krill) |
Fish and invertebrates (avoid mammal proteins – except beef heart or similar - which contain saturated fats) |
| Herbivore |
Cannot digest meats or most land plants |
Otos & Plecos (catfish), some African cichlids, tangs |
Live plants, seaweed, algae |
Plant-protein based - spirulina, algae, soybean meal |
Live aquatic plants, dried algae or seaweed, lettuce leaves, certain blanched vegetables |
| Omnivore |
Cannot digest some grains and plants (look for aquatic plants) |
Goldfish, Gouramis, Clownfish |
A variety of animal and vegetative matter |
Balance of meat & plant proteins (a good tropical or marine staple) |
A rotating combination of meat and vegetable supplements (above) |
Always look at the nutritional breakdown: the ingredient list and "guaranteed analysis" will give you an idea of how good a fish food is, and how much of it is filler!
| Analysis |
Purpose |
Recommended for Carnivores |
Recommended for Herbivores |
Note |
| Fat |
Primary source of energy |
No more than 8 % |
No more than 3% |
Avoid saturated fats found in mammals. Marine fish need a special kind of fat, "DHA", found in marine fish oil |
| Protein |
Include amino acids; key to health and growth |
around 45% |
15-30% |
Can come from plant or animal sources; Fry (babies) need 50% or more |
| Fiber |
Digestive health |
No more than 4% |
5-10% |
Commercial fish food is often low in fiber for less poop! Carnivores and omnivores don’t need much, but herbivores do, so supplement vegetables to help |
Other Content:
- Moisture and Ash: fillers that result from processing. Higher moisture means shorter shelf life. Ash contains essential and nonessential minerals, impurities and pollutants - it is a byproduct of processed bone matter, so diets formulated for carnivores usually contain more. Find the lowest moisture and ash content possible.
- Carbohydrates: again, used in processing as binding starches and fillers. Fish do not require carbs to function, though whole wheat is sometimes included as “roughage” to aid digestion. High carbs cause serious health problems. The lower the better.
- Phosphorus: Most fish need minute amounts of phosphorus, less than 0.9%, for proper growth. Any more than this and you are likely to have an algae problem, as algae consume this nutrient to grow.
- Calcium: bone and fish meals supply calcium, especially important to bone and tooth health if you have soft water. Good commercial foods supplement it.
- Carotenoids, Krill, Spirulina: Krill & Spirulina are natural color enhancers fish normally eat in the wild; carotenoids like beta carotene, canthaxanthin and astaxanthin may be artificially added but don't have a negative effect. (See testosterone, below).
- Testosterone: The male hormone testosterone is added to some commercial fish foods as a color enhancer. It produces unnatural colors and unpleasant physical and behavioral effects. Avoid it and look for one of the additives above instead.
- Vitamins: Vitamin deficiencies in fish as in any animal cause serious problems. Lack of vitamin A stunts growth and causes deformities. Vitamins E and A are needed to maintain breeding health. Vitamin K & H are needed for blood to clot and blood cells to form properly. Vitamin C aids digestion, bone and tooth health. Various B vitamins are important to normal growth and digestion.
Good commercial foods provide a mix of vitamins, but the variety needed explains why supplementation is important. Also, vitamin content of dried foods can quickly deplete over time. In addition to providing natural foods, using vitamin-rich additives is a good idea, especially in times of stress like when first introducing fish to your tank, or making any big changes. Vitamin additives are especially important if you feed your fish primarily on a diet of live, frozen or freeze-dried food.
Fish with upturned mouths, like bettas, feed at the water’s surface; fish with down-turned mouths, like catfish, forage along the ground; most other fish feed somewhere in the middle. The marine angelfish’s tiny mouth probes crevices in rock and sponge; feeding with a “grid clip” simulates this probing activity and encourages proper eating. Look up where your fish likes to eat to determine the format of food it would prefer.
(When choosing food size, use common sense: feed large fish large foods, like large granules or sticks; choose small or tiny foods for small fish, or crumble up larger foods.)
| Food Format |
Water Level |
Best For |
Notes |
| Flakes |
Floating |
Top Feeders |
Shortest retention of full vitamin and nutritional content. Replace every month. |
| Pellets or Sticks |
Either sinking or floating |
Sinking are good for mid-water feeders; floating good for top feeders, esp. those which find flake texture strange |
Usually larger; for larger fish |
| Granules |
Either sinking or floating |
Sinking are good for mid-water feeders; floating good for top feeders, esp. those which find flake texture strange |
Essentially smaller pellets |
| Wafers/Tablets |
Sinking |
Bottom-feeders and scavengers |
Usually made to meet nutrient needs of bottom-feeders |
| Liquids |
Circulates through tank* |
Filter feeders (e.g. corals, sponges) |
Often contain plankton, the microscopic natural diet of filter feeders. Generally for saltwater.** |
| Gels |
Usually slow-sinking |
Mid-level feeders |
Commercial gels often contain medications or ingredients difficult to create homogeneous dried food with.*** |
* Liquid foods can also be "directly" fed to your immobile filter feeders using a syringe-style manual feeder to bathe them in the liquid, ensuring that they are getting the full meal, especially in large tanks where it could take a while to get to them. Turn off protein skimmers when feeding plankton. More on this later.
** There are also liquid supplements and appetite enhancers for soaking dried fish food, but these are not foods themselves.
*** Homemade gels are popular with goldfish owners - the wide variety of foods that goldfish will accept includes meats, fruits and vegetables that are available at grocery stores, and the gel format allows you combine these for a balanced diet that won’t quickly disintegrate in your tank. Gels can be easier on a goldfish’s digestive system than some of the commercial choices.
Some of the most difficult fish to keep in an aquarium accept only live food, particularly marine fish. More commonly, live food is turned to when picky fish resist other forms of fish food. The movement of live food incites a predatory response in carnivores that other foods can’t match.
Live food can be difficult to obtain and feed regularly. For marine fish, freshwater feeder fish do not contain the right kind of fat to sustain them - DHA. (DHA is found in marine fish, more difficult to obtain as live feeders.) Moreover, live foods, whether fish or invertebrate, often have parasites, fungi or bacteria that could contaminate your tank. Most aquarists that use them have a highly trusted source.
Most people avoid live foods altogether, with the exception of foods like brine shrimp, which you can hatch yourself in a refugium or separate hatchery, and which are an excellent and irresistible source of fat and amino acids ideal for freshwater fry and occasional treats for fish. (Brine shrimp, unless treated, do not contain DHA fat, so cannot be used as a major part of any saltwater fish's diet, including fry.)
There are many high quality frozen foods available, which can be served on a feeding prong and wiggled about to entice predators. Almost anything you can feed live or frozen can now be purchased freeze-dried, and will retain nutrients and flavor for as long or longer, take up no freezer space and is generally less expensive. Chop it up if necessary for smaller organisms.
In nature, herbivores nibble or “graze” on various foods throughout the day – their tiny stomachs mean frequent, small meals are ideal. (Use a lettuce clip to hang a sheet of dried seaweed, algae, or lettuce into your tank for grazing.) Carnivores, with their large stomachs, may eat one large meal in several days. Fry and young fish need frequent feedings of protein rich foods like brine shrimp.
For herbivores and omnivores, keep feedings small. Feeding once a day is fine, although many aquarists prefer to feed smaller portions twice a day, sometimes even more. Feed as much as your fish consume within 3 minutes, and remove excess food with a siphon or net afterwards. For carnivores, if using a staple food, you can follow the same rule of 3 minutes – remember to supplement 3x a week!
For bottom feeders, “distract” the rest of your fish to ensure that they get their share. Do this by feeding floating or slow sinking foods to the rest of your fish first, then after a few minutes, dropping in the sinking wafer or tablet. Bottom feeders may need a little longer to get to their food, but you can still remove what isn’t eaten in 5 minutes.
Corals, sponges and other filter feeders that eat liquid diets of plankton should be fed phytoplankton during the day and zooplankton at night - this mimics the natural appearance of these foods on the reef. Both phytoplankton and zooplankton are major food sources for invertebrates in the ocean, so provide them both in the aquarium as well. Turn off protein skimmers when feeding plankton, and use a manual syringe for best results.
Some fish are nocturnal, like most catfish – it’s important to know if your fish are, as they’ll only feed at night! (Here's a general guide to common aquarium species to help you figure it out.) Feed them a little after you turn the tank day lights off. A normal photoperiod – day/night cycle – is important to normal feeding behavior in all fish.
Overfeeding is more common and more harmful than underfeeding – most fish survive for many days without eating, as they sometimes have to in the wild. Overfeeding leads to rapid pollution of your water – not just dirty or gross, the increase in ammonia when excess food breaks down could actually become fatal. Using an automatic fish feeder can help you control your feeding.
When going on vacation, an automatic fish feeder is simply your best option – “fish-sitters” have a tendency to overfeed since it’s a way to interact with the fish. Time release food blocks are improving in quality, but there is still a chance of pollution while you are away. If you must use a fish-sitter, pre-measure meals and label them so there is no guesswork – but an automatic feeder will be useful not only for vacations, but for your daily routine!
A FINAL THOUGHT
Just like with any pet, varying up their food and providing regular, natural food treats is not just healthier, it will make fish more colorful and more animated (happier!). Most fish are accustomed to a constantly changing menu in the wild and are more content with some variety. We want your fish to look their best and be healthy, hardy and energetic – you should too!
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