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Platy Problems: Dealing With a Bully

A Platy can make for a great starter fish, just be careful with the other fish you pair it with.

Are Platys Aggressive?

Our family home seemed empty, and like many others, we wanted a pet to liven the place up and teach the little one about caring for an animal.

After much consideration, we made the decision to purchase our first fish tank and set up an aquarium. We selected our gravel, a few smooth pebbles, a plastic reef, some plastic foliage, a little cavern for the fish to hide in, and a marimo moss ball.

We then carefully prepared our tank before purchasing our fish.

It took a couple of months to get the water levels right, mainly due to "new gravel syndrome," but once the conditions were okay, it was time to welcome some fish friends to their new home. As beginners, we didn't want to push our luck, so we researched the species that would do well in our tank.

A male Mickey Mouse Platy. You can tell the sex of these fish easily, as the female has a rounded fin on her belly (known as the anal fin), whilst the male's is pointed.

A male Mickey Mouse Platy. You can tell the sex of these fish easily, as the female has a rounded fin on her belly (known as the anal fin), whilst the male's is pointed.

Researching Our Species

We decided to set up our 10-gallon tank as a temperate freshwater aquarium, as this would be the easiest to take care of. When dealing with live animals, we didn't want to risk providing them with a habitat that was difficult for us to manage. Being new to the hobby of aquatics, we knew it was best to start off small!

After researching our species, we decided on Platys, and one Hong Kong Pleco. Described as colourful and placid, the Platy is a member of the Poeciliidae family, and like guppies and mollies, will give birth to live young.

We read up on their behaviour and learned that they like to be in a small group. Due to the size of our tank, we chose three females so as not to overcrowd them. We had been warned that bringing more than one male into the tank with a low female population would cause trouble as they fight for the right to breed. The males would also harass the females.

So the day came when we purchased our girls; a light orange one, a grey one with red markings and a "Mickey Mouse" pattern on her tail, and a dark grey one with a grey tummy and blue in the dark scales.

All of the fish settled well into their new home and dealt well with their water changes and tank cleans. One of them even gave birth, and our little aquarium was a joy for us all. But then the trouble began...

Aggressive Fish

Our fish soon relaxed and began to show off their own personalities. We chose names for them; Sunny for the golden one, Minnie for the grey one, and Goth for the dark one, as this fish enjoyed hiding in the dark before coming out and doing silly dances. If only we had known this dancing was a warning sign of things to come!

Sunny was a gentle and playful fish, always eager to engage with the other two. Minnie was easy-going, but Goth soon started showing some strange behaviours.

At feeding time, she would snatch a flake and steal it off to eat it away from the others. She would then chase the other fish away to make sure that she ate first. It became apparent that Goth wanted to be the dominant fish.

Shortly after, we hardly saw her, but a few days later, fry appeared. Could it have been hormones? The Platys were in a mixed tank when we purchased them, so she would have been pregnant. That might explain the chasing; we thought she was protecting her fry.

But no. She ate them.

Then the real fun started. Her aggression became more pronounced, and she would constantly keep her dorsal fin raised to show the other girls who was boss. Chasing, nipping, and charging at them, she would push them about.

We realised how serious things had become when Sunny stopped eating. A once cheerful and carefree fish now spent her days hiding in the cavern. Her colour paled, and whilst Minnie and Goth bulked up, Sunny seemed only half their size.

What could we do?

Suggested Solutions

We looked everywhere for advice. From internet forums to the aquarium where we purchased the fish, we tried our best to resolve this.

One suggested "time out" for the bully. This method involved catching the aggressive fish and placing it in a large container for a few hours. Then, rearrange the aquarium scenery, before returning the fish to the tank.

Another suggested putting a mirror in the tank so the bully would think its reflection was another fish; it would take out any aggression on the reflection.

To encourage Sunny to eat something, we also tried varying the diet more.

But nothing seemed to work, and as Sunny's health deteriorated, Goth started to take it out on Minnie.

A Sad Day

Finally, Sunny could take it no longer. The poor creature swam into the coral feature and passed away. We found her in the morning being cannibalised by the fish that had bullied her to death. It was heartbreaking.

I believe that the stress of being the victim of such aggression led to Sunny's death, and I could not look at Goth without disliking the creature. But it is just an animal doing what they do, so I had to think of a way forward to prevent this from happening again.

There was only one solution. Remove the bully from the aquarium.

I did not want to euthanise a perfectly healthy fish, so I had a chat with the store that I purchased her from, who took her back and gave me a voucher for a replacement fish.

So What Went Wrong?

I am still not entirely sure why Goth acted in this manner.

Platys have a reputation for being amiable fish that get along with each other. Only when you introduce two males to a tank would you normally see any sort of aggression.

I pored over expert advice, and I think the problem was caused by mixing varieties.

It turned out that Sunny was a Marigold Platy. These fish have a reputation for being friendly and chilled out. An older variety, they are less likely to display quirky behaviours that newer varieties might suffer from. Her nature sadly meant that she did not fight back and withdrew from the conflict.

Minnie is a Micky Mouse Platy, named because of the little mouse-shaped mark on her tail. These varieties have been known to be aggressive at times, but it is rare. Being of a tougher nature, she did not react to the stress in the same way that Sunny did and managed to stay out of the way and continue to feed and enjoy her aquarium.

Goth, I discovered, was a Platy/Swordtail hybrid. Probably a more recent variety, bred for its colour, she had a long "sword" coming out of her tail. Swordtails are renowned for being aggressive fish, and she had inherited this trait from one of her parents.

Mixing the varieties here seemed to be the cause of the problem.

A male Swordtail. These more aggressive fish can breed with Platys.

A male Swordtail. These more aggressive fish can breed with Platys.

Our aggressive Platy was very similar to this one, and may well be a Swordtail/Platy hybrid. Note the "sword spike" mark in her tail. Ours was even more pronounced.

Our aggressive Platy was very similar to this one, and may well be a Swordtail/Platy hybrid. Note the "sword spike" mark in her tail. Ours was even more pronounced.

Moving On

As upsetting as it was, we had to carry on as we still had Minnie and our Hong Kong Pleco to care for. Sunny had a fishy funeral, and Goth was returned in disgrace to the shop where she was purchased, where she will serve her sentence in fish quarantine before being re-homed with fish of her own variety.

A water change and deep clean of the tank have been carried out, and we will be obtaining some more fish to keep Minnie and the Pleco company. However, we will be sure that we purchase the more docile varieties, such as a Marigold or Red Wag.

Fish Get Stressed, Too!

If you have a bully, it needs to be removed. Fish are sensitive animals and the stress will kill the victims of aggression if you ignore this behaviour.

If you do not have the luxury of a spare tank, or a very large aquarium to which you can add more fish to break up the community a bit, speak to your pet store to return the animal.

Fish are living creatures, and I would not recommend killing a perfectly healthy animal because it ruins the vibes of your chilled-out tank!

If you want only one sex in the tank, choose females over males as the boys will fight.

If mixing the sexes, choose a male for every three females. More males will fight each other and will harass and stress out the females.

© 2015 Pollyanna Jones


Sandy on August 08, 2020:

Why platy fed their colour?? What can I do for that ????

I ❤️ fish on July 23, 2020:

I've got two male platys but i am not sure if I should introduce a male to the tank... I'm a bit worried because I've heard about male platys being aggressive.. Please help

Michael Cantu on April 03, 2020:

I killed my bully platy, fed him to the morning songbirds hanging around outside my bedroom window :)

Pollyanna Jones (author) from United Kingdom on January 29, 2019:

Hi Nanny Bum! Thanks for posting, and sorry to hear you're having trouble too. Having a same sex group is supposed to reduce in fighting, and these fish breed like mad. So you'd expect to see lots of baby platys if you added some girls. One of the girls we purchased was pregnant (they give birth to live young rather than lay eggs), and soon we had loads of cute babies. But to our horror, the adult platys ate them! :'(

Perhaps try adding some plants and terrain to the tank to help give them hiding spots and see if that calms things down? They're surprisingly territorial fish. Good luck!

Nanny Bum on January 26, 2019:

My daughter chose 5 Mickey Mouse platys to join our communal tank. We told the shop exactly what we had in our tank and were told the platys would fit right in. After 4 weeks, one of the platys is chasing all the others, nipping at them and generally bullying them until they were all hiding. I have taken naughty platy and put him in with my Siamese fighter whilst I find some help. The entire tank looks immediately calmer, however, now I’ve had a much closer look and consulted google images (c’mon, we’ve all been there) it appears as though I have bought 5 males!!

That’s problem 1.

Problem 2 is that said daughter is autistic and specifically chose those individual fish because of their certain colours so exchanging them is not really an option.

I’ve read that adding females should calm them down. Is this true? Any advice is welcome. My tank is 200 litres and has 32 small fish so I think I can fit a couple more in.

FishLover on November 26, 2018:

I have two betta male (snow) and female (kaleesi). I got a male and female platy to try get a community tank with kaleesi. Almost in an hour the male platty started harassing both the fish. I was surprised to see platy harassing my female betta. So I put him with the male betta. The male betta chased him around for half hour, once the male platty was calm and started hiding in the other tank I put him back to the community tank with other female and kaleesi. Now he looks very calm. It's almost like I thaught bully a lesson. Haha. Hope this helps for someone. Now I have a peaceful community tank and believe me the male bully platy is the calmest of all.

Isabella on August 05, 2018:

This is my second time around' and I am still opened for learning" Thanks'

Pollyanna Jones (author) from United Kingdom on July 17, 2018:

Thanks Glenn, it's pretty upsetting to see them do this. We have got by now with keeping the numbers down. I had no idea fish could be so territorial!

Glenn Stok from Long Island, NY on July 16, 2018:

I found this article extremely interesting Pollyanna. Well written and full of important details.

When I was young, I used to breed tropical fish. Guppies were my favorite. They were live bearers too.

I had occasions when two males would fight and literally tear fins off one another. I had to place them in separate tanks. This was a common problem, but only now have I learned what the problem was, thanks to reading your article.

Jennb on March 29, 2018:

My sunburst platy has just begun chasing and nipping at my painted platy. They are both males, and the sunburst platy is only targeting the painted platy. I just got two new fish two days ago (both female german blue rams) and I don't know if it has anything to do with that, but my case sounded a lot like this story, just one bully and one victim. They have been in a tank together for some time now, and this is completely new behavior. My tank is 20 gallons, and I have 9 fish, the sunburst platy (male), the painted platy (male), a blue wag platy (male), a velvet wag swordtail (female), three male guppies, one still a baby, and two female German Blue Rams. I do not have a great female to male ratio, and that is what worries me.

P.S- My sunburst platy is considerably larger than my painted platy

Sheilaomp on March 26, 2018:

My red wag platy is a terrible bully. He was chasing the female red wag around the tank so much that I added two other females. He chased those females around and bit the tail of one of them. The original red wag female starting chasing the new ones. The painted platy (that had its tail bitten died last night). The female that is gold and white is in a "safe" tank, but probably will not make it. Now I have 2 platys and 2 mollies. Both males are aggressive, but leave each other alone. They do not like new fish of any sex. The platys all ganged up on the weak fish. They actually circled it. So much for having an aquarium that is relaxing to watch.