Biology and Behavior

People often talk about “having the memory of a goldfish” to mean they’re forgetful, so it’s understandable that people think goldfish are unintelligent and wonder whether goldfish have brains at all.

And it’s certainly not a silly question. Did you know that not all animals do have brains?

For instance, starfish have a complex nervous system, but not a centralised brain. While jellyfish don’t have a brain or a central nervous system. If these aquatic creatures don’t have brains, maybe goldfish don’t either? Let’s find out…

Do goldfish have brains and how intelligent are they really?

You might be please to hear that the answer is yes – goldfish do have brains.

This diagram shows the location of a goldfish’s brain. As you can see, the brain is located at the top of the head, above the fish’s eyes, at the front of its spine.

And not only do goldfish have brains, they’re actually quite intelligent animals.

It’s myth that goldfish have bad memories. They can actually remember things for several months, at least.

Goldfish can also be trained to do tricks and behave in certain ways. For instance, pressing a button to get food. Goldfish wouldn’t be able to do this if they didn’t have a brain and at least a basic form of memory.

Goldfish are also socially intelligent. They are able to recognise and remember individuals – including humans – and they change their behavior around mates, potential mates and fish they know to be aggressive.

How big are fish brains?

While goldfish do have brains, their brains are not exactly huge!

A goldfish’s brain is about the same size as its eye. When you compare that to a human brain, you’ll realise that – proportional to their body size – the goldfish brain is really quite small.

This is the same for most types of fish. Most fish have brains that are about 1/15th the size of a similarly-sized mammal or bird.

In fact, it is a fish that holds the record for the lowest ratio of brain size to body mass. The Bony-eared Assfish not only has a very unfortunate name, it also has the smallest brain (relative to its size) of any animal with a spine (vertebrates).

There are some exceptions though. Elephantfish and sharks actually have quite large brains for their body size – about the same as birds and marsupials.

“Why do goldfish die?” It’s an important question to ask, because learning why goldfish die can help us understand how to keep them alive.

With proper care, goldfish have the potential to live a very long time.

In the vast majority of cases, there really is no excuse for a goldfish dying within weeks or months.

Our own research has shown that 80% of our readers have kept their goldfish alive for over a year – and some for much longer – but 1 in 5 goldfish keepers have never kept a fish alive beyond one year.

If your goldfish is dying – or perhaps your fish already died and you want to stop it from happening again – you’ve come to the right place.

Read on to find out why goldfish die and what you can do to keep your goldfish alive.

Why did my goldfish die?

Lots of people get in touch with us and ask “Why are my goldfish dying?”.

Sadly, it’s a really difficult question to answer without knowing a lot about the fish, its tank, its tank mates, and the symptoms it showed before it died.

There are lots of reasons why a goldfish might die. These include:

• Unsuitable living conditions: For example, keeping your fish in a tank that is too small, or not using a filter.
• Poor water quality: There are lots of water parameters that you need to balance to keep your goldfish healthy.
• Overfeeding: Goldfish really don’t need to eat much, and over-feeding can be very bad for them.
• Fighting with other fish: This can cause injuries and stress, which ultimately leads to illness and death.
• Accidents or injuries: For example, jumping out of the tank or getting stuck on the filter or in a decoration.
• Diseases: There are lots of infections and illnesses that can lead to the death of your fish.
• Old age: Of course, every fish dies eventually! If you’ve had your fish a very long time, it could simply have died of natural causes. However, bear in mind that goldfish have a very long lifespan.

If one of your goldfish dies, it’s important to work out why.

Understanding why your goldfish died will help you to keep your other fish alive, as well as any goldfish you may buy in the future.

But how do you identify the cause of your goldfish’s death?

My goldfish died… but I don’t know why!

Let’s look at some reasons why goldfish die, and the symptoms that allow you to work out the cause of death.

My goldfish died… and it has white or black marks on its fins and gills. Its fins look “clamped” together.

This sounds like a classic case of ammonia poisoning. Ammonia is a toxic chemical that builds up in your tank if it is too small or not properly cycled.

To avoid this in future, make sure to buy a big enough tank for your goldfish and that it is fully cycled (zero ammonia, zero nitrites, and less than 40ppm nitrates) before adding your fish.

My goldfish died… while near the top of the tank, looking like it was gasping for air. Its gills would move a lot.

This sounds like your goldfish suffered from a lack of oxygen and died because it was struggling to breathe. Make sure your Ph and KH aren’t too low and that there is movement in your water. This movement could come from your filter or from an air pump.

My goldfish died… and it had red lines on its tail and red marks on its body.

These red marks are a sign of nitrite poisoning. Like ammonia, nitrite is toxic to fish, and there shouldn’t be any in a properly cycled tank. You should therefore check that your tank is properly cycled to ensure this doesn’t happen again.

My goldfish died… and it had a big string of poop behind it a lot of the time.

Seeing your goldfish with a big trail of poop behind it is a sure sign of constipation. If your goldfish died after displaying this symptom, it was almost certainly because you gave it too much food.

My goldfish died… and it had raised scales, didn’t eat much and didn’t move much.

All of these symptoms are a sign that your water temperature was too high. Get a thermometer and check that your tank is in the correct temperature range for goldfish.

My goldfish died… after sitting at the bottom of the tank not moving or eating.

This could be a sign of shock. Did you change a lot of your goldfish’s water at once?

You should perform small, regular water changes, rather than big water changes. Sudden changes in water parameters can shock your goldfish, and potentially even kill them.

My goldfish died… and it had fungus on its body, frayed fins, and/or light or dark colored poop.

These symptoms could all be sign of an infection. You should therefore clean out your tank (assuming you have no other fish – if you do, watch your other fish closely to see if they show the same symptoms), cycle it again, and quarantine any new fish before adding them to your main tank.

My goldfish died… after being chased around the tank by its tank mates.

While this might look like playing, and is sometimes a sign of mating, it can be very stressful for the fish being chased. Goldfish don’t respond well to stress. It lowers their immune system, which can make them ill and potentially lead to them dying.

You should make sure that your goldfish is living with suitable tank mates. And, if not, be ready to separate your fish into separate tanks.

My goldfish died… and showed other symptoms not listed above.

It might be that your fish had some other illness or disease. We recommend reading through our articles on goldfish diseases to see if any of them match your fish’s symptoms.

What to do with a dead fish

If your goldfish died, you might be wondering how to dispose of dead fish. Whatever you do – please do NOT flush them down the toilet.

Flushing dead fish down the toilet can pollute the water in your area and risks spreading diseases to wild fish. This is not a responsible way to dispose of your dead fish, so please don’t do it.

Instead of flushing your goldfish, you should seal it in a bag and put it in the bin. It’s important to use a bag, as otherwise flies will lay eggs, which will hatch into maggots. You might get a bad smell too!

If you want a more dignified send-off for your fish, you could bury them instead. Why not have a little fishy funeral in your back garden?

Just be sure to get permission and bury your goldfish in a reasonably deep hole. You don’t want your fish to be dug up by your cat or wild animals!

How to keep goldfish alive

The best way to keep your goldfish alive is to do your research, learn a lot about goldfish, and make sure you’re at least doing the basics of proper goldfish care. Of course, The Goldfish Tank is here to help!

We recommend reading our article on mistakes that goldfish keepers make, as many of these can lead to the death of your fish.

Finally – learn from your mistakes!

We all get things wrong sometimes and very few people keep their very first goldfish alive for years. The important thing is that you learn for the future.

Two of the most common questions asked by goldfish keepers are “do fish have tongues?” and, if so, “how do goldfish tongues differ from human tongues?”

While it’s not essential to know about your fish’s biology. We find that taking an interest in questions like this helps people to better understand their pets. And, if you understand your pet, you can take good care of them.

Do fish have tongues?

Fish – including goldfish – do not have tongues. Or at least, not in the same way that people do.

Instead, they have a bony structure in their mouth called a basihyal, which looks a lot like a tongue and lies along the bottom of the mouth.

If you’ve looked closely at the mouth of your goldfish, you might have noticed it.

The basihyal has a very limited range of motion and few muscles, and it does not include taste buds. It’s therefore very different to a human tongue in every way other than its location in the mouth.

It is thought that the basihyal evolved as a barrier and additional layer of protection for the ventral aorta of the fish, which is very close to the mouth. The basihyal’s position helps to protect the ventral aorta from damage that could be caused by goldfish prey that thrash about or go down the wrong way when being eaten!

Human tongues are very strong and muscular, and perform a whole range of functions. We use our tongues to enable speech, to help us chew and digest our food, and vitally, to allow us to taste different things.

The surface of the human tongue is covered in nerve endings called taste buds. These are designed to detect different tastes, such as sweet, sour, salty and bitter.

The tongue is one of the main ways that we taste our food, as well as helping us to identify certain poisons!

So if goldfish don’t have tongues, can they taste their food?

Can goldfish taste their food?

Yes! goldfish can taste their food. In fact, over 20% of a goldfish’s brain is dedicated to its sense of taste!

You’ve probably seen your goldfish rooting through gravel and taking small stones into its mouth along with food. Along with its vision and sense of smell, a goldfish’s sense of taste is vital when foraging for food.

If a goldfish had to rely on eyesight alone then it would not always be able to tell the difference between gravel and food. However, using its sense of taste, the goldfish is able to separate the food from the gravel inside its mouth. This allows it to spit out the gravel and swallow the tasty food!

Do goldfish have taste buds?

Yes, goldfish do have taste buds. However, unlike in humans, goldfish taste buds are not located on the tongue.

In fact, goldfish don’t have tongues, so the taste buds have to be distributed elsewhere in the mouth. Goldfish have taste buds all over the inside of their mouths and they even have some taste buds located outside of their mouths, around their lips!

So, next time you see your fish skillfully separating inedible objects from pieces of food, you’ll know that a combination of eyesight, smell and a keen sense of taste is at work.

Also, knowing that your goldfish can taste its food is all the more reason to feed it a varied diet – you wouldn’t want to eat the same thing every day, so why should your goldfish?!

People often think that goldfish only ever grow to be a few inches long. Sadly, this is because most pet goldfish don’t live long enough to grow beyond this. However, with good care, goldfish have the potential to be much larger.

Common goldfish can easily grow to be 10 inches long and fancy varieties can reach 8 inches.

And these aren’t maximum limits! They’re fairly standard sizes, with some fish growing to be even larger…

How big was the biggest goldfish ever?

The wild goldfish pictured below was reported to be 14 inches long.

A pet goldfish in the UK was reported to be 15 inches long.

And the biggest goldfish ever recorded – the official world record – was a gigantic 18.7 inches!

These potential sizes are why we encourage all of our readers to buy a good sized tank or to keep their fish in a pond. It’s vital to ensure they have plenty of room.

While it is true that fish will become stunted if kept in smaller tanks, we consider this practice to be cruel and bad for your fish. You should always give your pets the space they need. This allows them to grow to their full potential.

Why do they get so big?

Genetics is a factor. Some individuals simply have the potential to grow bigger than others depending on their genes.

However, all healthy goldies could grow to several inches long if they receive the right care.

Goldfish will naturally grow to a large size when they are well looked after and given the right conditions to live in. These conditions include plenty of pond or tank space, good water quality, warm water temperatures and a supply of nutritious food.

Goldfish Growth Rate

The average growth rate of a goldfish is about one inch per year.

There are ways to make your goldfish grow even faster, but remember: you should always aim to provide your fish with the best possible care.

You shouldn’t try to stunt their growth to keep them small or overfeed them to make them grow. You will only end up harming them.

That said, if you really want a big goldfish – and you want to make them grow faster – there are some things you can do to safely influence your goldfish’s growth rate.

Next, we’re going to explore the five factors that influence growth rate.

How do you make goldfish grow faster?

The key to making goldfish grow faster is a good diet combined with lots of tank space, warm water temperature and good water quality.

It also helps to choose fish with the right genetics. Though you will need to go to a specialist breeder to have any chance of knowing whether your particular pet had large parents!

Let’s look at the five factors that influence goldfish growth rate in more detail.

#1: Nutrition

Having a good diet is very important.  Serious breeders feed goldfish fry a high protein diet of live foods, such as micro-worms and baby brine shrimp. This stimulates growth and helps to produce the largest fish.

The runts in a spawn, who do not get as much food as the others, will not reach the size of their siblings. Because of a poor diet when they were young, some fry will never reach more than a few inches long for the rest of their lives.

A nutritious diet plays a big part in growth rate throughout your fish’s life. This is why feeding good food is a must.  Live foods and veggies, in addition to a good protein staples, like pellets, can help your fish grow.

However, you must be careful to never overfeed them! Overfeeding will pollute your water and cause your fish to become constipated.

#2: Tank Size

Many goldfish have the potential to reach an impressive size, but then their owners buy an undersized tank or add too many fish.

Not having enough tank space will stunt your fish’s growth. Their activity will be restricted, meaning they get less exercise, and growth inhibiting hormones will build up in a tank that is packed with too many fish.

Sadly, stunted goldfish are permanently impacted and the damage is irreversible. You therefore need to give your fish plenty of space from a very young age and throughout its life.

#3: Temperature

Temperature plays a big role in growth rate.

Goldfish kept in warmer water temperatures consume more oxygen, eat more food and are generally more active. All of this helps them to grow to a large size.

Water temperature in the mid-70s Fahrenheit (mid-20s Celsius) is ideal.

#4: Genetics

As we mentioned earlier, the growth potential of your fish is limited by their genetics.

Unfortunately, unless you are a goldfish breeder, you really can’t do much about this one!

All you can do is buy your goldfish from a quality breeder, rather than a chain store. This will give you a better chance of finding a fish with good genes and which hasn’t already been stunted by poor conditions.

#5: Water Quality

Maintaining good water quality is not only vital to your fish’s health, it plays a role in their growth too.

When toxins are present in the water, goldfish cannot grow normally and must channel their strength into surviving. You can get rid of these toxins by cycling your tank and doing weekly water changes. This will improve your water quality and allow your fish to put more of its energy into growing big and strong.

How big is your fish?

Add a comment to let us and other readers know how big your largest goldfish is.

Goldfish aren’t as playful as cats and dogs, you can’t pet them, or take them out for walks, but you can engage with them in other ways – and even train them!

How to train your goldfish to eat from your hand

Yes that’s right, you can feed your fishy friends directly from your hand!

Simply hold your hand out with the food in your fingertips and, eventually, the fish will take the food.

Over time, your fish will get more used to this, until they start to beg for food and head straight for your hands when you put them in the water.

How to train your goldfish to do tricks

You can even get goldfish to carry out simple tricks. Using food as a reward system is the key.

For example, place some food in your fingertips at the end of a hoop and watch your goldfish swim through the hoop to get the food.

Repeat this technique until the fish has got the hang of it. But remember not to overfeed your fish as this can be fatal.

Eventually, the fish will start to associate the hoop with food and will regularly swim through.

Let your goldfish invent their own tricks

Goldfish are more interesting to watch if they have an engaging atmosphere to swim around. They will enjoy their habitat more and may even invent a few tricks of their own!

Invest in goldfish tank decorations and you might find that your fish likes to swim under bridges, through driftwood or round and round their castle!

Keep it fun and good for your fish

You should enjoy bonding with your pet fish. Make their home special, feed them nourishing food, and even use their food to train your pet. Just remember to always have the best interests of your fish as your top priority.

Never try to force your goldfish to do things they don’t want to do – or that might harm them – and never over-feed them during food training.