How Much And How Often Should You Feed Your Goldfish?

by Adam Till


Short Take

Let our little goldfish paste give you a quick intro...

There are two popular questions when it comes to feeding goldfish:

  1. What's the best food to feed my goldfish to get the best growth?
  2. How much should I be feeding each day?

The first question is answered in this article, and the second is what we'll explore together now.

Quick Navigation

I'll happily admit that the way things get done around here is NOT the way that most people feed their fish.

If you're looking for the "spoiler alert" version of how to feed your fish so they look as good as ours, it's to feed:

  • 1.5% of body mass per day for adults
  • up to 4% of body mass per day for babies
  • soft foods or a mix of hard and soft foods to avoid floatyness, constipation and swim bladder issues
  • the above amount spread over multiple feedings per day

In a nutshell, most people feed the wrong things, not enough, and not frequently enough.

After all, if you have an 8oz adult oranda like pictured here:

Zhao oranda with ryukin friends measures 8oz

Each day's feeding for this fish alone is going to be one of these choices here (each portion measures 0.12 oz, which is 8 oz x 0.015):

Each of these portions is 1.5% of bodyweight for that oranda above

Does that look like what you're feeding?

We'll get to the reasons for all of that soon enough, but let's just quickly address the elephants in the room first.

Feeding According To The Label

If you read the instructions on most goldfish foods, they at least tell you to feed multiple times a day.

Breeders have proven that if you feed multiple times a day in small portions vs once a day as a single meal, even if the total amount fed in a day is the same, you'll end up with better growth from the multiple meal arrangement.

The part that gets tricky is the next recommendation - how much to feed.

In this article we're going to look at three foods:

All three are amazing foods, but if you were to go out and buy them today not having owned a goldfish before, you might be a little confused by the feeding instructions.

According to the label:

  • Northfin pellets: "Feed 1-3 times daily, only as much as the fish will eat in 1-2 minutes"
  • Omega flakes: "Feed three times daily, feeding only as much as the fish can consume in 2 minutes"
  • Repashy Super Gold: (*crickets*) no feeding instructions

Helpful? Nope, didn't think so.

What happens if my fish is slow? What happens if my fish is a little on the blind side (moors and telescopes)? Why do the different foods have different instructions, and why doesn't Repashy say anything?

Okay, so that's not useful so far.

Feeding According To The Web

So if you're a little confused, if you're like most people your next step will be to head to the web.

As a random sample of website advice though:

  • "A time frame of about 30 seconds is all most goldfish keepers should be aiming to feed in. Any more than that… and you are actually risking your tank." (puregoldfish.com)
  • "Feed 2-3 times daily. In terms of the amount to feed, a good rule of thumb is to only feed an amount that the goldfish can consume in under two minutes or only feed as much as the size of the goldfish’s eye." (Australian RSPCA)
  • "A good rule of thumb is to feed your goldfish no more than he can eat in about one to two minutes. Goldfish can literally eat themselves to death, so you need to be very careful that you do not need overfeed your goldfish. Feeding him up to three times a day should be sufficient. Grab just enough food that you can easily pinch between your thumb and index finger. " (wikihow)

Oh good, a new series of suggestions given with more random reference points thrown in. Let's look at our new suggestions.

Time

Here again, we're all over the place. Apparently somewhere between 30 seconds and two minutes. Again, what happens if he's slow or a little blind? Do they need less food?

About As Much As the Eye

"About as much as his eye" - well that's random. If you poke around a little you'll find that this normally comes from a notion that a fish's eye is about the same size as its stomach.

Spoiler alert: it's not.

Whether the pouched structure attached to their intestine can be properly described as a "stomach" is a matter of debate (pro here and con here...I vote with the vet as pro), anyone that's done a necropsy (dissection) on a goldfish can attest that the organ and tract is FAR bigger than the fish's eye.

Just a Pinch

Cool, feed as much as I can easily pinch between my thumb and index finger. What if I have tiny hands, or big mits? What about with Repashy...a pinch of soft gel is a messy proposition, and I'd rather use a spoon thanks.

Feeding According To Science And Experience

Luckily for those of us like you and I that like to have instructions we can actually  follow, there are much easier instructions around that have been refined by breeders with experimentation and experience.

If you want the most unbiased and scientifically measured information on feeding fish, the best place to look is the commercial aquaculture industry.

Commercial Aquaculture

After all, whether they're raising salmon in the ocean or catfish in freshwater, commercial operations have to be efficient about converting food into fish because they make money that way.

The faster and quicker a farm can grow a fish while keeping it healthy, the more money they can ask for the final fish.

The downside to reading aquaculture literature like this article here is that they usually default to talking about feed efficiency. Feed efficiency is a measure of weight of food fed to weight of fish created, and though intellectually interesting, is sort of hard to wrap your brain around when you only have a 40 gallon goldfish tank in front of you.

Koi Keepers

Luckily for us, our friends in the koi world take things just as seriously as the commerical fish growers do, but have a habit of making things easier to understand on a small scale.

A wonderful study was done back around 2004 in Texas, and they were nice enough to publish their work on the web for the rest of us to appreciate (link here).

The article itself is a fascinating read, and talks about feeding for different life stages, and even using differnet nutritional blends at different times of the year depending on whether the weather is getting warmer (sping) or colder (fall).

Since most people keep their fish all year around in the same temperature, however, this is likely the most relevant take away for you as a goldfish owner:

70F – 85F - Increase feeding of low protein food to 1.0% up to 1.5% of total koi body weight as water temperature rises.

Koi and goldfish are similar enough that the work translates well, and we're finally getting to numbers we can relate to.

It's easy enough to measure the weight of a goldfish:

...and a little bit of math then gets us to an answer (more on this later).

Hikari Research Lab

When we visited California in the summer of 2018 to attend Goldfish Palooza 2018 (writeup here), one of the talks we got to attend was given by Chris Clevers, president of Hikari USA

Hikari has an entire reseach lab in Japan dedicated to testing their (and competitor's) foods in order to determine the best possible mixes for goldfish and other aquarium fish.

Although their bagged products carry the same marginally helpful advice as other companies ("Feed 2 to 4 times daily, the amount your fish will consume within a few minutes."), as a result of an audience question (*grin*) in the presentation Chris mentioned the same sort of statistic that the koi keepers did above:

"We've found the best growth rates from feeding about 1.5% of bodyweight daily, up to about 1.8% for young fish or breeding fish" (paraphrased from talk)

Now we're on to something!

How Much Should I Feed My Goldfish?

If you want to have a good, easy to follow guidline for how much you should be feeding your fish, feed them about 1.5% of bodyweight per day spread into as many feedings as you can consistently deliver.

So for an 8 oz mature large oranda, you'll be feeding one of these portions (not all, one...they're shown together to show how much of each type weigh the same):

The amount of food you should feed an adult oranda goldfish that weighs 8oz per day

Are you surprised by the relative amounts of food pictured there? Most people are! Typically, most people overfeed pellets and gel food, and underfeed flake.

Flake in particular is so light that I've seen people starve their fish to death while thinking they're borderline OVER feeding.

We don't feed flake much, but out of curiosity I fed the above amount to a our big 125 tank (where it made quite a mess). The fish hunted down all the specks, but it definitely took a while! I'd wager they were hunting down flake for over an hour, and that's only feeding the amount of flake appropriate to ONE oranda; there are five fish in that tank!

If you try this experiment yourself with bigger fish, you'll quickly realize that the notion of "feeding as much as they'll eat in two minutes" is pretty ridiculous. Fish can eat WAY more than what measures out at 1.5% of bodyweight in pellets or gel in two minutes, but way less than what they'd need in flake.

Ever wonder why lots of goldfish seem to do well when small, but not as well as adults? 

Measuring Your Fish

In order to weigh your fish, find a small kitchen scale that measures up to a few pounds. Most of us have one in the back of the closet somewhere, but something like this will do just fine and basically costs less than a can of food from most pet stores (click the image for more details):

To weigh the goldfish:
  1. Find a container of water that will fit your fish comfortably
  2. Move the scale and container near your aquarium
  3. Fill container with tank water, and place the water and container on the scale
  4. Touch the "tare" button on the scale, which will zero out the reading. Any weight you add from that point will be shown on the display
  5. Catch your goldfish in your hands or with a net, and place it gently in the container
  6. Record the measurment

Ta da! Nothing crazy there.

Next, you'll need a slightly more accurate scale to actually measure out the food since the number will be very light. Again though, the scales are ridiculously affordable, and are useful for both food and weighing out medicines (or spices in the kitchen, click the image for more details):

 Use this formula with a pocket calculator:

Weight of goldfish x 0.015 = weight of food required for one day

So if our goldfish from before weighs 8 oz:

8oz x 0.015 = 0.12 oz of food per day

Does This Apply To All Sorts of Foods, or just dry foods?

Feel free to mix and match between different foods, as long as the total weight comes out to be what you calculated. It's actually quite a good thing to have a variety, since it keeps things moving in their digestive systems.

When measuring Repashy gel, the conservative thing to do is to measure the food powder before hydrating it (adding water). The above photos show the food being measured after adding water, but the difference isn't THAT much in the end.

Likewise, if you feed frozen food like daphnia or bloodworms, technically you'll need to drain off the liquid before measuring. We don't bother to do that on a regular basis, but when you're getting a feel for how much to feed it's worth the extra step.

The only exception to this is that when it comes to vegetables and such should you choose to feed them (we don't), there isn't really much of a practical limit besides making sure not to let things rot in the tank. They're not strictly required, however.

Do I Have to Prepare The Foods Beforehand? A Spotlight on Goldfish "Swim Bladder Syndrome"

EDIT If you've had a chance to read some of the other articles here that talk about swim bladder issues, you'll already be aware that the biggest causes of what people term swim bladder include

  1. structural issues
  2. blocking the opening
  3. too much bacteria
The goal is to keep the gut moving, and then you won't have bacteria levels skyroc and smaller meals or higher quality/more digestible foods make that much easier to accomplish.

My previous article on choosing a healthy food or foods for your fish already touched on sinking vs floating, but suffice to say I don't personally put much stock in the rumor that floating foods cause swim bladder issues. As stated in that article the biology just doesn't support it, and neither does both my experience and that of a number of my colleagues.

Likewise, people are often warned to soak even their sinking food beforehand, lest the foods expand in the stomach and cause issues. Again, there are a number of arguments against this practice.

First of all, particularly with flake, the longer the food is submersed the more prone the food is to losing water soluble vitamins and other nutrients.

Second, if all food needed to be presoaked to save fish lives, most breeders would go out of business since it isn't possible to use wet food in automatic feeders.

Lastly, the more of a "process" it is to feed, the less likely you are to feed more often. A single large meal or low quality dry food may be less dangerous to feed presoaked, but a high quality food with relatively few fillers and binders fed frequently isn't a danger in the first place.

Do you like handling stinky bowls of soaked and swollen fish food? No? Then maybe don't bother.

So although the advice to "prepare" the foods in advance is well meaning, it's simply not required with a balanced, high quality diet. Research that Hikari has done in particular really supports that most health issues come from dirty tanks, bad water, and cheap food than it does to any particular style of food, and my experience mirrors that.

Switching Foods

If something you've read has inspired you to change your feeding products lately, you may have experienced the unfortunate side effect of your fish turning up their noses and refusing to eat.

Even if you try over a few days, sometimes the little darlings will still insist that you're trying to poison them and refuse to eat.

First of all, be sure you're removing all uneaten food (other than vegetables) every day to avoid spoilage. If they didn't eat a pellet etc the first day, they're probably not going to, and the oils and proteins will make these foods prone to spoil quickly at the temperatures most of us keep our tanks.

You can try to blend foods into each other as well, or even soaking the new pellets in the "juice" from frozen bloodworms and or appetite enhancers like Seachem's Garlic Guard.

Those products are for nice people though...the other (and more effective) option is just to starve them out.

Although I recommend that you vacuum out all uneaten prepared foods every day if they aren't eaten, if the only thing you offer your fish is the new fish, eventually they'll get hungry enough to eat.

When they realize they aren't going to die, they'll usually just switch over to the new food.

The process is almost universally always harder on you than it is on them, but be assured that goldfish can easily go weeks without food, and if you're offering it everyday, you're not exactly starving them anyway.

Tough love is a good thing!

Fish Food Storage Best Practices

Interestingly enough, the way people store their food can play a huge part in the supposed "preferences" for food that their fish supposedly display.

Though there will definitely be foods that are more or less readily taken by certain goldfish, the easiest way to almost guarantee that they go off their food is to let it go rancid at room temperature by storing it next to the aquarium. You wouldn't willingly eat spoiled food, and your fish doesn't want to either.

If you look at the label for the average fish food, you'll notice that most of the top ingredients of good food have something to do with fish or seafood related products.

In the same way that you wouldn't expect a fresh tuna to sit out on the counter for too long before funking up the joint, ideally you'll treat prepared fish foods with the same respect. They haven't come up with a preservative that'll keep things going for too long without the oils starting to go rancid, and it's best not to test the technology in the first place.

As a rough guideline, if you can treat the food like people food, you won't go too far wrong.

That means:

  • store in the fridge if your family is nice, or at least somewhere cool and dry
  • don't expect to feed out of the same giant Costco-sized container for months no matter how it's stored. Air exposure also makes things go off, so break the giant containers down into smaller ones and freeze the others (or just buy the smaller sizes more frequently).
  • if you accidentally thaw frozen food, throw it out if it's not used. Likewise, only unfreeze what you're going to feed within a reasonable period of time. Freezing doesn't prevent food from spoiling, it just halts bacterial action for a while. The act of thawing speeds that up into overdrive, so one thaw and you're done.
  • keep it away from the warm and humid fish tank!

Adjusting Feeding Your Goldfish For Temperature

How Often Should I Feed My Goldfish?

Essentially, if you feed the above recommended amount spread over the day, you can't feed too often.

If you place the amount of food aside in the morning and throw in a pinch every time you pass the tank, that's great!

If you have multiple tanks or aren't home very often, a good compromise is:

  1. feed in the morning
  2. use a autofeeder like the Eheim Everyday Feeder (about the only one we recommend, also available from Aquarium CoOp) to feed two other times during the day
  3. last feed before bed

That's about 4 times a day, without too much effort.

Make Sure Your Filter Can Handle The Change!

A Note On Travelling and "Fish Sitters"

How Much Should I Feed My Goldfish If I Want The Most and Fastest Growth?

The answer to this question is actually more layered than you might think.

Since goldfish are not machines, you can't just add more food and always get more growth...that's not how metabolism works.

There's generally accepted to be an upper limit of somewhere between 1.8% and 4% depending on age and temperature where extra food isn't going to do very much beneficial for the fish.

While goldfish are technically known as indeterminate growers (meaning they never stop growing their entire lives), breeders like ourselves have found that goldfish do most of their meaningful growing within the first year of their lives. After that a lab or a sensitive scale may be able to measure the growth of the fish year over year, but the visual changes won't really be all that noticeable.

As a result, if you haven't managed to get hold of the fish when it was really young, or if it's formative months weren't very fish friendly, then you may not be able to do very much by "power feeding" them.

Growth is also limited by the hormones in the water which limit growth, and the overall quality of the water. That's why breeders use huge ponds or do daily changes like we do in order to flush these limiting wastes from their grow out operations.

Temperature plays a huge role in determining how much growth a fish will put out, and it's not surprising that the hugely inflated, borderline mutant-looking giant ryukins and orandas that can be found on the web generally come from extremely hot countries like Thailand and Malaysia.

Lastly, there's a significant argument to be made for welfare concerns when it comes to pushing fish too hard for growth. Scientific studies like this one have proven links between manipulated growth rates in fish which end up limiting life span, so your fish may pay a cost in living a shorter life if you push it too hard with changes in growth.

What If My Fish Don't Look Right Following These Guidelines?

Absolutely feel free to adjust to suit your own fish!

If you're sure that they're not constipated or outright sick, the usual reason that fish will fail to thrive when on a good feeding program is that there's something else stealing all the food that you're adding.

If it's another fish, some people will teach the fish to eat out of their hand so that they can regulate how much goes to each animal. Other people will float a colander in the tank, add the slow feeding fish there, and feed the groups separately.

A less obvious source of something else stealing food is if the fish is wormy or parasite laden inside. This is part of why our regular quarantine routine includes things like PraziPro, which is specifically designed to get rid of worms like this.

The Value Of Consistency

Whatever program you choose to follow, try to be as consistent in your feeding amounts as you can. Adjust amounts for your fish as it grows, by all means, but try not to get too off the wall with changes of amount or food.

The more consistent you are with feeding after all, the easier it will be on your filter and water change routine.

You'll also be able to spot changes in your fish's behavior better, and you'll be able to notice little issues before they become big problems.

In the End

Although it may seem odd to be told not to feed according to the label on your food, hopefully you can see where the advantage of having a baseline measurement like 1.5% of bodyweight daily will come in.

After all, you've never been told to "only eat as much thanksgiving turkey as you can comfortably finish in 3 minutes", or to limit your desert to a portion "the size of your eye", and to do the same with your fish makes about as little sense.

Now do I honestly think that most people will do this? Nope, not really!

It's even unreasonable to expect people to do this all the time.

If you do take the chance to follow these guidelines, however, you might just end up with a winning ribbon at your next fish club competition!





Adam Till
Adam Till

Author



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