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Why Do Goldfish Chase Each Other? (How to Find the Root Cause)

Why Do Goldfish Chase Each Other? (How to Find the Root Cause)

The purpose of this blog is to share general information and is written to the author's best knowledge. It is not intended to be used in place of veterinary advice. For health concerns, please seek proper veterinary care.

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Many people set up aquariums for their relaxing and peaceful ambiance. But sometimes, the inside of the tank is about as restful as a playground of children high on sugar and caffeinated soda. There the goldfish go, chasing each other like some warped game of tag. Why do goldfish chase each other?

Goldfish chase each other for a number of reasons, including the tank is too small, mating, playing, lack of food, or illness. Goldfish are rarely aggressive. Thus, if a goldfish is obviously not playing or trying to woo, then there is something wrong, and it will need to be fixed.

Goldfish are typically the aquarium equivalent of the Dude in The Big Lebowski. They’re usually the chill fish, telling the rest, “This aggression will not stand, man.”

Thus, if your goldfish are chasing each other, it is essential to establish why. But it isn’t always easy to know without looking for particular signs.

Reasons Goldfish Chase Each Other

It isn’t easy to guess why goldfish have gone from the Dude to something out of Game of Thrones, but it is crucial to make sure it isn’t due to lack of space, food, or if they are in poor health. Even mating can be cause to intervene if several males are harassing the female.

Is the Tank Too Small?

Goldfish are notoriously kept in tanks that are too small. Part of this stems from the myth that goldfish simply grow to fit their tank. Unfortunately, goldfish kept in small tanks are not only being stunted, but it can also make them cranky and aggressive.

A single goldfish requires at least a 20-gallon tank, and many goldfish breeds require a 100-gallon tank or large pond. Since goldfish require friends (they are socially chilled fish), it is typically recommended that goldfish be kept in groups of five or more. This means the tank needs to be roomy.

A sizeable tank isn’t just important to keep goldfish from becoming aggressive. Lack of oxygen in the water can also occur. The other major issue is that goldfish create a substantial amount of bio-waste, which can cause illness if the tank is too small.

Thus, if your goldfish are chasing each other with nips and bites, assess the breed and the number of total fish in the aquarium. Anything under 20-gallons is definitely too small. But, since most breeds require a minimum of 20-gallons and another 10-gallons per fish, you most likely require a 50-gallon tank or bigger.

Are They Mating?

Unfortunately, when goldfish males become amorous, they don’t present the focus of their affection with the fish equivalent of chocolates and flowers. Instead, it looks like the World Wrestling Entertainment is playing their own version of pool-tag. It’s a crazy frenzy that looks like anything but love.

Making matters more confusing, domestic goldfish kept in a tank are not like wild elk with a distinct mating season. You can’t check the calendar and go, “Ah yes, that’s why my goldfish is acting like piranha scenting blood.” Instead, many things can trigger the urge to mate, including a water change, regardless of the time of year.

Thus, to know if your fish are in heat, you have to observe the chaos and determine if it is male fish chasing the female fish. During mating, it is always the boys chasing the girls, not the other way around. However, trying to tell a goldfish’s sex is not easy, but there are some clues.

Male goldfish develop breeding stars on their gills and fins when they’re ready to mate. Breeding stars are scattered white dots. It’s kind of looks like kids when their acne bestows tiny blackheads across their face, except this is white dots on vibrant colored scales.

When males are chasing a female, their aim is to bump the female’s soft belly to get her to push eggs out. There could be some nipping and tugging involved to the fins, but it’s the bumping of her abdomen that’s their true aim.

The female fish will have a swollen vent where her bio-waste (fish poo) is normally excreted. The male’s vent is flush against his body, under his tale, and can hardly be detected. The female’s when in heat, will poke out like a tiny lump.

If you see a goldfish releasing wispy white streams from a vent, that’s a male releasing milt, the equivalent of sperm. Where a female goldfish might be laying tiny white dots against plants, and these are her eggs.

Mating can be rather hard on goldfish, and fins can get torn. Therefore, it is generally advised to have three females for every one male in your tank. Otherwise, the females can get seriously hurt. Which sounds all well and good, but goldfish are not like getting a puppy where you can check their sex with a glance between the legs. Thus, if you do have too many boys and too few girls, you need to separate them until they chill out.

Are They Playing?

Goldfish don’t tend to play a lot, but they might, especially when bored. If they chase each other for fun, it won’t be one-sided, with one fish always doing the chasing. Nor will it be territorial, with a specific fish only chasing when a tank mate wanders into a particular area. Lastly, they won’t be nipping, biting, or trying to hurt each other.

Is There Enough Food?

Goldfish are not typically aggressive over food. Nor is underfeeding fish a common problem. But there are fish breeds out there that can be very aggressive about food and display food dominance. Occasionally, a goldfish might display food dominance too. This might include chasing fish away when they try to eat.

Rarely is food dominance due to lack of food. People notoriously overfeed. However, experimenting with feeding times and types of food might fix the issue. For example, a bully might gobble its favorite, say pellets, and leave the flakes for the others.

Also, ensure that the food is distributed in different spots during feedings, not sprinkled in one section. Hopefully, the dominant fish will focus on eating its favorites in its preferred area and allow the rest to eat too in other sections of the tank. Also, it might be more aggressive during certain times of day and quieter in others.

You can put in a tank divider to keep the food bully in its own section if no other option seems to work. Sometimes this only needs to be temporary until the younger fish grow or new fish gain confidence in the tank.

Lastly, some people don’t feed their fish often enough, only a few times a week. They believe it cuts down on the amount of bio-waste. This is not recommended for fish happiness and health, however. Thus, consider feeding them 1 – 3 times a day in smaller amounts, if you are not already.

Is the Fish a Jerk and a Bully?

While goldfish are not commonly the bullies of the tank, it does happen on occasion. Fish do have personalities, and sometimes the personality is unbecoming. Thus, if your tank is roomy, everybody is healthy, there is plenty of consistent food, and nobody is trying to make babies – it is entirely possible you’ve got a bully-goldie.

If you have a bully, there are really only two options. The first is to use a tank divider and keep the bully and some fish it isn’t mean to (hopefully, there are a few) on one side. If for whatever reason, that isn’t possible, then a second smaller tank for the bully and possible friends to dwell in might be necessary.

Is It Illness?

Goldfish can, at times, become aggressive if ill. Thus, if the goldfish is being cranky and chasing its tank mates like they are the spawn of Hades, you need to assess if your fish is healthy. If the fish isn’t, then appropriate action should be taken.

People used to think there was little to be done if a goldfish was doing poorly. Maybe you moved the tank to a less sunny spot, adjusted the food, checked the water, but that was about it. Now, there are plenty of options, including performing surgery on a goldfish.

Many goldfish problems can be fixed by simple things, such as medicine obtained from a pet store and added to the water, changing infiltration systems or tank water, or moving an ailing fish into a separate tank and treating it there. But sometimes, you need a vet’s professional advice.

Those in the United States can find a fish-friendly vet by contacting the American Association of Fish Veterinarians. They can give referrals or, depending on the matter, provide advice online or over the phone. There are similar organizations in other parts of the world, including the UK’s Fish Vet Society which has a list of aquatic vets.

Parasite or Breeding Stars?

Sometimes those white spots are not breeding stars. Ichthyophthirius multifiliis is a common ailment in goldfish caused by a parasite. This condition is typically referred to by its nickname “ich.” The parasite is tiny, and it fastens itself to fish, both the scales and fins. The parasites eat and reproduce, leaving visible salt crystals on the fish.

If you already know which goldfish are male and female, it is obviously not breeding stars if the female fish are showing the white spots. However, if you are not sure of your fish’s sex or know it is a male but are uncertain if he is displaying breeding behavior, there are some clues if closely observed.

For starters, if you start seeing the white spots at the tail end, and there is nothing yet on the face or gills, then it is most likely to be ich. Breeding stars tend to cluster on the front half of the fish’s pectorals, fins, face, and gills.

Also, males in heat are focused on female fish, chasing her around, bumping her belly. When a fish has ich, the fish’s skin is irritated and will start “flashing,” darting around for relief. They will be trying to rub away their discomfort, zipping to various places and rubbing themselves against tank ornaments, equipment, and even the side of the tank.

Why Is My Goldfish Hanging Out at the Tank’s Top?

Goldfish chasing each other isn’t the only maybe-fine-maybe-worry behavior a goldfish might display. Another common stunt is to hang out at the top of the tank.

Goldfish, unlike other fish, don’t have a preferred depth level for their species. But if a fish is constantly hanging out at the surface when it isn’t feeding time might mean your goldie is about to shove off this world. They’ll be pretty still, looking dopey rather than chilling.

However, if the fish looks like it is gasping for breath, it could also be because your water is low on oxygen. Test your tank, and you might need to change 30% of the water and evaluate your aeration and filter systems.

Once you’ve changed the water and ensured the aeration and filter systems are in proper working order, your goldfish’s behavior should return to normal. However, if it is still gasping at the top, then it is sadly likely to be ill.

That said, if your fish just comes to the surface whenever you get near the tank, being frisky and not looking stressed, then it’s probably fine. Goldfish can be like dogs, hoping for unscheduled snacks. They are also social in their own way and sometimes just want to come “closer” to where you live out in the open.

Again, so long as the fish isn’t looking listless or gasping and only coming up when you are near the tank, then your fish is probably fine. But if it is always up there looking pathetic, your fish most likely needs help.

Final Thoughts

A goldfish chasing another goldfish does not always mean something is wrong. Goldfish can play chase occasionally and will chase when feeling the urge to mate.

But it will require some observation to ensure that the goldfish isn’t chasing for reasons such as having too small or tank for being unwell. But if you are concerned, there are specialized vets to help.