Top 10 Mistakes New Fish Owners Make – #7

The #7 Mistake – Feeding Your Fish Too Much

One of the more common “healthy” pet issues we see in all of veterinary medicine is obesity, and fish are no exception. They may have better control than your golden retriever, but overfeeding your fish can have more severe consequences than just rounder fish.

Unfortunately, there is no absolute calculation to tell you how much to feed your fish. It depends on their species, temperature, water quality, other stressors, the type of food, formulation and current disease processes. For cats and dogs, it all depends on body size and life stage. If you take any bag of cat or dog food and look at the back, it will tell you what life stage the food is intended for and what amount to feed for body weight. (This assumes that your pet is the correct weight for the body type and structure.) But when was the last time you weighed your pet fish? Fish should be fed based on body size, but we know this is an impossible task for most owners. Thankfully, fish are pretty good at determining when they are full. A bigger problem is what happens when there is too much food in the tank.

So what should I do to ensure my fish are not overfed? We recommend using the 5-Minute Method. It is very simple:

  1. Sprinkle a little bit of food into your tank. We recommend mixing it close to the filter return so all fish can get a fair share.
  2. When all the food is eaten, sprinkle a little bit more. If the food is not completely consumed, WAIT.
  3. Continue for 5 minutes or until the fish stop eating.

NOTE: Some species, like betta fish, are not great at regulating their intake. Keep in mind that their stomachs are about the same size as their eyeballs. Only a few pellets once or twice a day is adequate!

Why does this method work?

The biggest problem with overfeeding a fish tank is not just fat fish, but increased stress on your biological filtration. The breakdown of fish food, since it contains a lot of protein, causes an increase in the ammonia levels in your tank. Using this method makes sure that the food ends up in the fish, not the bottom of their tank. If you’re unfamiliar with ammonia and the nitrogen cycle, read this explanation.

For more information on fish food in general, watch our webinar.


What do I feed my fish?

If you own any pets, I guarantee you have fallen victim to pet food marketing. It happens to all of us, even veterinarians, causing us to question the education we received on just this topic. “Grain free,” “gluten free,” “all natural,” “organic” and other buzzwords are dropped at lightning speed to confuse the consumer into purchasing based on just how many of these words can fit on a package. And fish diets are no exception. Sure, they may not get the press of the cat and dog food, but a lot of little containers can fit into a very small shelf, causing fish owners eyes to glaze over just taking in the sheer magnitude of choices. Many owners will be drawn to either the flashiest packaging or cheapest price. It’s just a fish, right? Well, just like the food you eat yourself and feed to your fluffy pets, fish rely on good nutrition in order to stay healthy. By purchasing a quality fish product, you can improve your fishes’ lives significantly.

So how do I choose a quality product?

The best consumer is an informed consumer. We have a great webinar that is recommended by many of the top fish food companies. It breaks down how to read the labels on the back of fish food containers. There are considerably less items to peruse than your regular box of supermarket crackers.

Don’t have time to watch? Let’s break it down to the simplest parts.

Pellets vs. Flakes

This rule is easy to follow. If a pellet fits into your fish’s mouth, go with the pellet. This is due to surface to mass ratio and water soluble vitamins. Consider how much contact a flake has with the air and water in comparison to a pellet. A big, wide flat flake will lose more of its water soluble vitamins, including vitamin C, faster than a concentrated pellet. No matter how long the container has been open, pellets win.

The 6 Month Rule

I don’t care what is printed on your container; after you break the bag or jar open, you have 6 months to feed that food, then toss it. At the end of those 6 months, the water soluble vitamins, again, are so reduced, you might as well be feeding your fish cardboard. Those dates are printed on the outside in the event the store doesn’t sell the food by then.


This is listed on the ingredient list as “crude protein,” “crude fat” and “crude fiber.” This does not refer to petrol and is instead the method of testing.


All animals need protein to survive. Fish can be herbivores, omnivores or carnivores. Herbivores and omnivores need between 35-45% protein in their food. Carnivores require 40-55%. The protein source must contain all essential amino acids for the fish to live. The best source of these for fish is animal protein, specifically fish meal. Fish meal is any leftover fish scraps from processing fish into other products, mostly for human and cat consumption. Fish meal is perfectly safe and healthy. The best plant source is soy, but this can only make up 50% of the total protein. Soy does not contain all the essential amino acids fish need to survive.


Fats are used for energy, insulation and hormone production. In most fish, fats should be 15-25% of the total diet. Just like humans taking fish oil supplements, fish also require N-3 fatty acids that they cannot fabricate themselves. Vegetable oils have very few N-3 fatty acids. Fish can become obese with overfeeding, so try not to feed your fish your love!


The primary energy source in food is poorly digested in fish. High levels of carbohydrate rich treats can actually cause liver malfunction. Omnivores should only have 25-40% of their diet from carbohydrates, whereas carnivores require <20%.


Fish require most of their water and fat soluble vitamins from their diet. This includes vitamins A, C, D, E & K. Vitamin A deficiencies can lead to skeletal deformities, and lack of vitamins C & E decrease immune function. As we mentioned previously, these vitamins are the first nutritional component to leech out of food pellets and flakes.

Minerals (ASH)

No, ash does not mean that charcoal particles are mixed in as filler. Ash measures the mineral content of the diet. Most fish get their minerals from the surrounding water, so there is very little need for supplementation in the diet. Phosphorus is one of the main requirements from food, but only 0.3%.

Spotting Quality Food

Consider the various protein sources in a bag of fish food. If there are additional protein supplements listed, or multiple protein sources, this indicates a poor protein source and therefore, poor quality diet. Know the scientific names of all the vitamins and make sure your food contains all the essentials. A “vitamin mix” is perfectly acceptable.

Color Enhancing Food

Some koi diets contain color enhancers to bring out the red pigments in the skin. This is done through the addition of carotenoids, including synthetic materials, yeasts, bacteria, fungi, krill/shrimp and algae. These foods should be few very sparingly and only a short period of time.

How much to feed?

You’ve heard of our 5-minute rule, yes? You can apply it to all fish, not just koi. Always consider the size of the stomach in a fish. Provided you are not reading this zoomed in, the stomach on your betta fish is only this big –> o It’ll only take 4-5 of the tiny pellets and 1-2 of the larger pellets to fill that stomach. Bettas are repeat offenders for eating too much and not being able to pass large balls of poop. We are happy to recommend different feeding strategies based on your system.

If you have any questions about fish food, please contact our office directly: or (831) 346-6151