Goldfish Aggression, Bullying, and Rough-Housing

Understanding why your fish are picking on each other.

Are your goldfish not getting along?

Bullying and aggression is something that worries every fish-parent because most times, we don’t know how to handle it.

Leaving the fish to “fight it out” is definitely not an option.

We certainly can’t reach right in and separate them like we do our children, although it would be a quick and easy solution!

It helps to understand factors that may be contributing to their grouchy demeanor and how to intervene. 

Let’s figure out why you have goldfish aggression, bullying, and rough-housing going on in your tank!

HOW DO YOU KNOW IF THEY ARE PLAYING OR FIGHTING WITH EACH OTHER?

Goldfish are social and enjoy interacting with one another. 

However, there are different characteristics to look for when trying to decipher if they are playing or bullying.

Play

  • Swimming AROUND each other, not AFTER each other.
  • Darting AWAY from each other, not TOWARDS each other.

Aggression

  • Nipping at other fish
  • Butting other fish
  • Coming after other fish from another area within the tank (territorial)

WHAT CAUSES GOLDFISH TO BE AGGRESSIVE?

When we think of bullying and aggression, one of the first things that pop into our heads is the playground bully.

You have to wonder why they pick on other kids! Well, it typically comes down to what kind of environment they are being raised in. 

In applying that principle to goldfish, there are influences within the tank environment that can provoke aggression and bullying.

Some of which can be prevented.

CAUSE #1

Putting Fast Swimmers And Slow Swimmers Together

PREVENTABLE…

One of the number one things to prevent aggression and bullying is to use caution in what type of goldfish you put together.

THERE ARE TWO GROUPS OF GOLDFISH THAT SHOULD NEVER BE PLACED TOGETHER.

1. STREAMLINE-BODIED (FAST SWIMMERS)

  • Common
  • Comet
  • Shubunkin
  • Wakin

2. EGG-SHAPED (SLOW SWIMMERS)

  • Fantail
  • Veiltail
  • Butterfly Tail
  • Telescope Eye
  • Celestial Eye
  • Bubble Eye
  • Lionhead
  • Oranda
  • Pompom
  • Ranchu
  • Ryukin
  • Tosakin
  • Pearlscale

Fast-swimming (streamline-bodied) goldfish tend to pick and nibble on the slow-swimmers (egg-shaped/fancy.)

At feeding times, fast swimmers compete for food almost always leaving little or nothing for the slow swimmers. 

CAUSE #2

Too Many Fish In One Tank - Overcrowding

PREVENTABLE…

how many goldfish can i fit

We can only imagine the frustration and stress of living in a one-bedroom apartment with 20 other people!

Now picture that with goldfish.

They are trying to find a solitary and peaceful little piece of real estate within a crowded tank to relax, but there is no such thing.

The stress that overcrowding causes goldfish will cause territorialism and competition for food.

Don’t put too many fish in one tank. 

There are guidelines on how many goldfish can adequately go into a tank.

It’s all based on the size the fish will reach as an adult as well as the dimensions and size of the tank.

Size of Tank

Fast Swimmers (Streameline-Bodied)

(size at maturity = 6-9”)

Slow Swimmers (Egg-Shaped/Fancy)

(size at maturity = 9+”)

5 Gallon

1

Tank Too Small

10 Gallon

1

1

20 Gallon

2

1-2

30 Gallon

3

2

55 Gallon

5

4

65 Gallon

6

5

75 Gallon

8

7

100 Gallon

11

10

155 Gallon

17

13

CAUSE #3

Mating

The mating ritual of goldfish can be quite aggressive and appear as if one is picking on the other. 

For those unfamiliar with goldfish mating, it may seem like the mean kid on the block is bullying the nice kid!

The male goldfish continually chases after the female to cause her to lay her eggs.

This game of chase can last a while, so be prepared!

Monitor them to ensure the male is not injuring the female. She can grow weak from the constant quest making her vulnerable to him nipping her on the tail and fins. 

In our world, we would have laid those eggs a long time ago to get that bully off our backs!

CAUSE #4

Disease And Stress

PREVENTABLE…

sick goldfish

When a goldfish is stressed, it becomes prone to disease. Stressors can be prevented to avoid disease.

However, disease can creep into a healthy tank when introducing a new fish that is diseased.

If you notice a sick fish in your tank, move it over into a hospital tank to prevent the other fish from picking on it.

Read up on goldfish diseases and how to treat accordingly.

STRESSORS (THAT LEAD TO DISEASE) 

  • Poor water quality
  • Overcrowding
  • Placing the wrong type of goldfish together
  • Introducing a new fish that is diseased
  • Placing the tank near a TV or stereo speakers

WAYS TO PREVENT DISEASE

  • Maintain healthy water parameters through routine water testing, water changes, and tank maintenance.
  • Don’t put too many fish in the tank.
  • Don’t put fast swimmers with slow swimmers.
  • Quarantine new fish in a separate hospital tank for a few weeks before moving to the community tank.
  • Place your tank in a location that is not directly near sunlight, loud sounds, or high traffic.

When All Else Fails, Separate!

If you happen to notice aggressive behavior in your tank, watch the fish carefully to rule out any of the above causes. 

There comes a time when you may have no other option but to remove the bully and put it into another tank.

Sometimes you just have to bite the bullet to protect your other fish!

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