Goldfish Overfeeding – 5 Risks You Should Know About

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Goldfish are some of the most exhilarating tank fish for good reasons. They’re hardy, peaceful, adapt well to community tanks, and come in over 200 species, each with countless color, size, and shape variations.

Goldfish are a great choice for both novice and more experienced aquarists looking to add some diversity to their tank.

They are generally easy to care for, so long as you understand the basics of fish maintenance.

Some useful tips in this sense include:

  • Ensure stable temperatures, around 68 to 74 °F, since goldfish rank as cold-water fish
  • Keep ammonia and nitrites to 0 since even the smallest amounts of ammonia could hurt or even kill your goldfish
  • Perform regular tank maintenance, as often as necessary, to eliminate food leftovers and excess fish waste
  • Change 10-15% of the water every week to preserve the system’s stability and oxygenate and clear the water
  • Provide goldfish with a nutritious and diverse diet, ensuring optimal nutrient intake

Today, we will discuss the latter, jumping on one of the most widespread problems novice aquarists deal with: overfeeding.

This is a volatile problem since goldfish have no natural limit when it comes to eating. They will simply eat as much food as they can find.

So, expecting them to stop eating once they’re full can cause some unwanted surprises. Most novice aquarists deal with this problem as it mostly stems from their good intentions.

They want to care for their goldfish as best they can and, in the process, end up feeding them more than they’re supposed to.

As we will see, overfeeding comes with some rather serious problems along the way.

Problems With Overfeeding Goldfish

Learning how to feed your goldfish properly is essential for providing them with a stable and healthy lifestyle.

Otherwise, they can experience several health problems, such as:

Swim Bladder Disease

This disorder has multiple causes, including parasites inflaming the organ, other organs swelling due to various diseases and pressing against it, birth defects, and even overfeeding.

The latter is what interests us, especially since it may seem out of place. What does the swim bladder have to do with what goes into the stomach?

As it turns out, it has a lot to do with it. The swim bladder is located on top of the stomach, and it’s usually very long, 2-3 times the stomach’s length. If the stomach inflates, it will press against the swim bladder, forcing the air out of it and affecting the fish’s buoyancy.

Goldfish don’t have stomachs, as their food goes straight into their intestines, but the same principles apply nonetheless.

As I’ve already mentioned, several issues will cause the stomach to grow large enough to affect the swim bladder, but overfeeding is of particular interest. That’s primarily due to what overfeeding means and how and in what circumstances it affects the fish.

In this sense, we have:

  • Eating too fast – If the fish is very hungry, it may consume too much food too fast. The same happens when there are other goldfish around, leading to fierce food competition and causing the fish to experience FOMO (Fear Of Missing Out). This will cause the goldfish’s intestines to grow fast, pressing against the swim bladder.
  • Eating too much at once – Even if the fish eats at a reasonable pace, it does no good if it eats too much. The same problem will occur.
  • Constipation – Constipation can result from overeating, parasites, or even ingesting large chunks of food that clog the intestines. This issue will expand the intestines or the stomach, pressing against the swim bladder’s walls and affecting the fish’s buoyancy capabilities visibly.
  • Gulping too much air – This generally happens with floating foods that remain on the water’s surface. If the food doesn’t sink, your goldfish will have to collect it from the water’s surface, gulping air in the process. This will inflate the fish’s digestive system artificially, and it can happen quite fast too.
  • Extremely cold water – If the water temperature is low enough, the effectiveness of the goldfish’s metabolism will drop significantly. In that case, even providing the fish with its normal food ratios could fall into the overfeeding category.

As you can see, the notion of overfeeding displays quite a handful of variations, making it more complex than it may seem.

Swim bladder disease comes with several symptoms, such as:

  • Difficulty swimming straight
  • Bloated belly and a curved back
  • Difficulty remaining afloat and sinking to the bottom
  • Difficulty staying upright as the goldfish constantly turns on its side or upside down

If your goldfish displays signs of swim bladder disease, consider assessing the condition’s causes.

Depending on the causes, you can devise a reliable treatment plan involving increasing the water temperature, allowing the fish to fast for a couple of days, and offering boiled and skinned peas for a plus of fiber.

You can even use antibiotics if the condition has to do with parasites or bacteria.

Bloated Belly

If your fish’s bloated belly is the result of overfeeding, the situation isn’t as severe, but it still requires immediate treatment.

If you’ve eliminated the possibility of pregnancy, ammonia poisoning, or other unrelated issues, the problem may lie in overfeeding.

Several problems link to an unusually bloated belly in goldfish, including:

  • Swim bladder disease – We’ve already gone through this. I would say you should treat this disorder the same way you would treat constipation. The reason for that is that swim bladder disease doesn’t come with any disorder-specific symptoms, so it may be difficult to diagnose it accurately. It’s simple – if your fish displays a bloated abdomen, consider the treatments you would use for any digestive problem.
  • Constipation – This is a natural outcome of overfeeding, especially in goldfish, seeing how they lack a stomach. This means that they have less space to store their food, and they need to eat smaller portions with several hours in between. This will provide their digestive system enough time to break down the food and eliminate the waste properly. Overfeeding goldfish will forcibly stack the intestines with food, overburdening the digestive system, and constipating the fish.
  • Impaction – Impaction is the term we use for the aggravation of chronic constipation. If your goldfish experiences constipation too often or the problem is too severe, the clogged poop may dry out and get stuck in the intestine. At this point, the fish may not be able to poo anymore, causing a bloated abdomen for goldfish and plenty of headaches for you.
  • Getting obese – Yes, fish can get fat due to overeating, although this doesn’t happen overnight. All animals are prone to becoming overweight or obese if eating too much, and goldfish are no exception. Overfeeding them will lead to fat accumulating on their organs and under the skin, leading to a bloated look. In this case, reversing the process may take time since your fish will need to lose its excess weight and get in shape.

The solution is simple. If your fish displays a bloated abdomen, consider adjusting its feeding pattern. If you’re not overfeeding your fish, the problem may be elsewhere.

Cloudy Water

This is quite an annoying effect since nobody wants their tank water murky and cloudy. While this problem is usually the result of poor tank maintenance, there are factors that will exacerbate the effect considerably.

Overfeeding is one of them. But why is that, and what triggers the cloudy-water effect? In short, bacteria.

Every aquatic environment will contain a biofilm comprising of billions of microorganisms, some beneficial, others not so much.

We’re interested in the latter since these can disrupt your environment’s stability and even affect the fish in the process. Overfeeding results in a lot of food residues and fish poop, a problem that’s that much more severe with goldfish, which are notoriously messy.

This excess organic matter will serve as food for the bacterial colonies, allowing them to multiply fast. The more they are, the murkier the water will become. This will not only disrupt the tank’s esthetic appeal but your fish’s lifestyle as well.

The good thing is that the fix is relatively easy. Cease the overfeeding, perform a water change, and clean the habitat of excess fish waste, food residues, and any other dead organic matter. This should clear up the water fast.

Also, prevent overfeeding moving forward, otherwise, the issue will return.

Algae Growth

Anybody who’s ever had a fish tank knows that you can never eliminate algae from an aquatic environment.

You can control their spread and inhibit their development partially, but you can never eradicate them. Algae rank as plants since they use photosynthesis to support their vital processes.

They also rely on organic matter to thrive, such as decaying food residues resulting from overfeeding. The excess food will accumulate on the substrate and feed the generation of algae, which will bloom fast, depending on the environmental conditions. This can impact your tank’s ecosystem fast.

The water will become murkier as the algae spread over the tank’s walls, decorations, substrate, and even plants and will even affect your fish.

Algae will not only compete with plants over the same resources, but they also consume valuable nutrients from the tank’s water.

This behavior will affect your goldfish, depriving them of the minerals they need to remain active and healthy long-term. You can easily prevent this problem by avoiding overfeeding, to begin with.

If you notice algae overgrowth in your aquarium, perform an immediate cleanup to remove the excess, do a water change, and adjust your fish’s feeding pattern.

Only feed your goldfish enough food for them to eat within a 2-3-minute window.

Ammonia Level

This is the deadliest problem to consider on today’s list. Ammonia is poisonous to fish even in small amounts and can turn deadly fast.

But what’s the connection between overfeeding and ammonia?

This chemical builds up in the tank from 2 sources:

  1. Fish – The fish themselves produce ammonia, but not the way you think they do. Most people believe that fish produce ammonia via their poop, which is only partially true. Only a small amount of ammonia is produced that way, and it’s generally not enough to cause any serious threat to the environment. Unless you have a lot of fish, producing a lot of poop. In reality, most of this chemical is produced immediately via the fish’s gills. This process is the result of the fish’s body breaking down the protein and producing ammonia in turn.
  2. Bacteria – Overfeeding results in a lot of excess food sinking to the substrate and decomposing over time. Much of it gets buried in the substrate, out of sight, where the tank’s biofilm breaks it down, producing ammonia and nitrites as byproducts. The tank’s bacteria will flourish as a result which will accelerate the process of ammonia buildup even further.

Normally, you should have a filter to dilute ammonia and support the cultures of beneficial bacteria that feed on this chemical.

But when it comes to goldfish, the filter may not suffice. Overfeeding your fish constantly will lead to a fast ammonia buildup, outweighing your filter’s ability to counter it.

Not even weekly water changes won’t be able to do the trick. The only solution to the problem is to stop overfeeding the goldfish altogether. This is exactly what we will discuss next.

How Often to Feed Your Goldfish?

I would say up to 3 times per day at most. Some people recommend 2 meals, but that usually varies. Not all goldfish display the same appetite or require as much food.

When it comes to feeding your goldfish, I would say you have several options to consider.

You either feed them enough food for your goldfish to consume within 3 minutes, twice per day or as much as they can eat in 2 minutes, 3 times per day. Which option is best depends on your goldfish’s species, size, and appetite.

You may also need to feed your goldfish more often if you have a larger community with many goldfish housed in a large tank.

More frequent feeding will make sure all fish get access to food so that no one starves. Providing enough food will also lower food-related competition and aggression since goldfish are notorious for fighting over their meals.

As a plus, consider that the goldfish’s age also comes into play when planning their meals. Goldfish fry, for instance, tend to eat smaller but more frequent meals since they require a regular influx of nutrients throughout the day.

They will gradually eat less frequently with time, ending with just one meal per day in their senior years.

How to Feed Goldfish to Avoid Overfeeding?

This question has several answers or, if you like, one answer divided into several parts.

Here’s how to approach the feeding aspect when it comes not only to goldfish but fish in general:

  • Small and frequent vs. large and rare – I believe this to be the golden rule to preventing overfeeding. It’s always better to feed your goldfish more frequent small meals because that’s how the fish is used to eat in the wild. Wild fish almost never have access to large quantities of food and will eat small portions several times throughout the day. I recommend replicating this behavior since it will feel natural to goldfish. Go for 3 small meals per day, rather than 1 or 2 larger ones.
  • Control the quantity – Your goldfish should eat most if not all of the food within 3 minutes. However, since goldfish will display different appetites, I recommend experimenting with this aspect. Feed your goldfish a set amount of food and watch how much it takes to consume all of it. You can adjust the feeding pattern based on the findings. If the fish eats all of the food within 2 minutes, provide slightly more food next time. If there are too many food residues, cut down the meal size.
  • Provide adequate food – Goldfish are omnivorous, so they will consume a variety of foods, both plant, and animal-based. That being said, these fish have quite distinct food preferences. Even if the food is technically right for your goldfish, the goldfish may not like it. And just because it likes it, that doesn’t mean that more is better. Make sure the food is right for your goldfish and that the fish likes it. Otherwise, you will have more food residues than necessary.
  • Remove excess leftovers – This is a must, especially in the first phase, when you’re still getting acquainted with your goldfish’s feeding habits. Eliminating excess food residues will decrease the need for frequent tank maintenance and take some weight off your filter’s metaphorical shoulders.


If there’s anything you should take from today’s article, that would be the idea that you should never trust your goldfish’s instincts.

These fish display unmitigated appetites and will easily consume more food than they should.

In fact, goldfish are probably the easiest to overfeed, especially due to them lacking a stomach and requiring more time to digest their meals.

When it comes to feeding goldfish, I recommend sticking to the basics. In short:

  • Feed small quantities of food, enough for your goldfish to consume in full in less than 3 minutes
  • Provide up to 3 meals per day, depending on your fish’s age, appetite, and how many fish you have
  • Always offer palatable food that your goldfish enjoy
  • Ensure optimal nutritional intake
  • Clean food leftovers regularly

These measures should both prevent overfeeding and eliminate the risks associated with excess food waste.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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