Jack Dempsey Fish: Completed Care Guide

This is one of my all time favorite fish in the hobby. They’re big and fierce, with bright colors and great personalities.

But, they’re not for everyone.

In this guide, I’ll teach you everything you need to know about Jack Dempsey fish so you’ll know if they’re right for you.

Jack Dempsey Overview

Jack Dempsey Cichlid in Aquarium

The Jack Dempsey (Rocio octofasciata) is a cichlid native to the freshwater streams and rivers of Mexico, Belize, Guatemala and Honduras. 

There are established populations in the United States, Australia and parts of Asia. It is considered an invasive species in these areas and was most likely introduced when aquarists released pets into the wild. 

What do Jack Dempsey fish look like?

An adult Jack Dempsey is truly stunning. 

They are oval-shaped fish, longer than they are tall, that have large dorsal and anal fins with a big rounded tail.

Their base color ranges from a dusky, rosy pink all the way to a dark almost black color.

They are covered in metallic, iridescent blue/green spangles that are extremely eye catching. These spots reflect light and flash brightly as the fish swims.

Dempseys have always been one of my favorite species. The way they shimmer and shine seems almost unreal, like something that spectacular couldn’t possibly be natural.

Then there are also captive bred color varieties, known as electric blue Jack Dempseys, that have much larger patches of the iridescent blue/green. They almost look like a completely different species of fish.

The older and larger the fish gets, the more pronounced the iridescent spangles become.

Since they grow to be very large fish, they are definitely a centerpiece species that can be noticed from across the room.

Their size, color and feisty personalities have made them a favorite in the hobby for decades.

How big do they get?

Big. Really big.

In the wild, males usually top out at 12 inches (30 centimeters) and females get up to about 10 inches (25 centimeters).

If they’re given enough space in an aquarium, you can expect that males will get up to about 10 inches long and females will top out at 8 inches (20 centimeters).

Pro Tip: Fish can’t reach their full size potential unless they’re put in a large enough tank. Being kept in a smaller tank will stunt their growth. Remember, bigger is always better when it comes to aquariums.

And Dempseys aren’t just long, they’re also a very thick-bodied, bulky fish. So a 6 inch Dempsey has a much higher bioload (the amount of waste that enters the water) than a slim bodied 6 inch fish, like a silver dollar.

Keep this in mind when you’re looking at tank size and filtration levels. I’ll go over both of these later in the article.

How long do they live?

Dempseys can live 10-15 years, so bear in mind that you’re making a long term commitment if you decide to bring one home.

Preparing and Setting Up Your Jack Dempsey Tank

Aquarium Size

Be prepared that you’ll need to provide a really big tank if you want to keep this species. For a single fish, I would recommend a 55 gallon (208 liter) tank as the absolute bare minimum.

Bigger is always better when it comes to aquariums, especially when you’re housing large fish.

If you want to keep a pair of Dempseys, a 100 gallon (378 liter) tank would house them nicely. 

If all this seems like it’s just too big of an investment for you, think about going with a smaller species of fish.

Equipment

Filtration

Filtration is one of the most important parts of your aquarium. 

I’ll give you a brief explanation of why and how it’s even more important when you keep large fish like Dempseys.

Fish constantly put off waste into the water that surrounds them. And the bigger they are, the more waste they produce.

All that waste sinks to the bottom of your tank where it starts to break down, putting off ammonia (NH3). This is a bad thing since even a small amount of ammonia is toxic to fish and invertebrates.

Lucky for us fishkeepers, there are beneficial bacteria that live in our filters. One kind eats ammonia and turns it into nitrite (NO2 -1), another toxic byproduct. But then another species of bacteria quickly eats the nitrite and puts off something called nitrate (NO3-).

This whole process is known as the aquarium nitrogen cycle.

Nitrate is much less toxic and can be allowed to build up in the aquarium in between water changes.

Pro Tip: Getting the nitrogen cycle up and running in a new tank doesn’t happen instantly. For more information on how to get your tank ready for fish, check out our steps for performing a fishless cycle.

But, you need a filter with the capacity to process all that waste. The filter needs to be large so it can house a big enough population of beneficial bacteria. That way, you have enough bacteria to eat up all the ammonia produced by a ginormous fish. 

And it needs to be able to pump enough water so dissolved wastes come into contact with the bacteria. 

Without a big enough filter, there aren’t enough bacteria on hand to deal with all the poop. Then rotting waste will put off deadly ammonia as it breaks down in the tank, eventually making the water unlivable.

And Jack Dempseys are big fish. So they put off huge amounts of waste. 

I really recommend that you go with an oversized filter to match your oversized fish and its monster-sized poops.

I also don’t think there’s such a thing as over filtering your water. So go with a filter that can easily handle the volume of your tank and then some.

And you can even get some extra filtration by adding on something like a sponge filter

Related: Best Aquarium Canister Filter

Heater

In the wild, the Jack Dempsey fish’s natural habitat ranges from Mexico to Honduras, very warm environments. 

So a heater is an absolute must for these big guys.

It’s better to go with a slightly oversized heater than an undersized one. A puny heater will constantly struggle to keep the water warm enough. That means it will have to stay on almost constantly to maintain the temp.

I’ve found that this really shortens the lifespan of a heater.

And since they’re one of the pricier pieces of equipment in your tank, you want them to last as long as possible.

Related: Best Aquarium Heaters Reviewed

Plants, Substrate and Decor

Plants

OK so if you have plans for a big, beautiful planted tank, this is probably not the fish for you. Jack Dempsey fish, just like a lot of cichlids, love to dig in the substrate. 

I like to even out the gravel after a water change so it looks all nice and level. I once watched a Dempsey I owned spend hours digging out a hollow and mounding up the gravel all around it. By the end of the day, he’d dug up more than half of the tank.

Some owners don’t have much problem with Dempseys ripping up plants, while others say it seems to be the fish’s mission in life.

And there’s no way to know which kind of fish you’ll end up with.

They don’t necessarily eat the plants, the way a severum will, but they will dig them up and drag them off when they want to rearrange the tank.  

They’ll leave floating plants alone, like hornwort, water sprite, pennywort, frogbit or water lettuce, but anything rooted in the substrate is vulnerable.

Related: Best Aquarium Plants

Substrate 

For Dempseys, I’d recommend going with either sand or gravel.

Since they like to dig, a planted soil substrate would end up being a huge mess since they would break it apart.

Also, in my opinion, they look better against a dark substrate

They’ll change their color to match their surroundings. So instead of washed out purple/pink color, their base color becomes very dark, almost black.

This makes their iridescent spangles stand out even more.

I recommend a dark brown or black substrate so your fish will darken up. 

Also, it’s best to go with an inert substrate. Don’t use substrates sold under the heading of “cichlid sand.”

Cichlid sand is made of aragonite, a crystalized form of calcium carbonate (CaCO3). I don’t want to bore you with too much of a chemistry lesson here. Suffice it to say that aragonite sands constantly leach calcium carbonate into your water, which increases, the water’s hardness and pH.

The increased mineral levels are great for African cichlids that love hard water, but that’s not really the best for soft water cichlids like Jack Dempseys.  

It’s better to use an inert sand for Central and South American cichlids.

Related: Best Aquarium Substrate For A Planted Tank

Decor

Jack Dempsey fish need a mix of open swimming areas along with large pieces of decor that they can use to establish a territory and as a place to hide.

They definitely appreciate having a roomy cave that they can retreat to when they feel threatened. 

Once they’re full size, large rocks or pieces of driftwood that they can hide behind make good hiding spots. Mine would hide behind some big rock work I had in the tank whenever he got scared.

Ideal Water Parameters

The native waterways of this fish are very soft and tend to have an acidic pH.

However, Jack Dempsey fish are tank bred fish, so they are able to adapt to a wide range of water conditions.

  • Temperature: 74°-85°F (23°-29°C)
  • Ammonia/Nitrite: 0
  • Nitrate: <40 ppm
  • pH: 6.0-7.0
  • GH: 3-8 dGH (50-133 ppm)
  • KH: 4-6 dGH (72-107 ppm)

Temperament and Tank Mates

Jack Dempsey fish really aren’t great candidates for most community tanks. 

They can be very aggressive and tend to become increasingly territorial as they age. And they’re more than big enough to harass and kill most other fish.

Dempseys will usually stake out a territory in a cave or behind some driftwood so they have somewhere to retreat to if they feel threatened. 

They’ll guard this area and try to drive away any fish that wanders too close. 

They always kind of remind me of stereotypical tough guys from movies who stand on the corner and defend their turf.

It’s possible to keep a mated pair together in a large enough tank. They may still beat each other up a bit from time to time, but more than likely they will just hang out together peacefully.

Pro Tip: Mated pairs will not tolerate other fish in the tank while they are breeding. They will destroy other fish with extreme prejudice. It’s best to keep a breeding pair in their own tank.

But you absolutely cannot keep two sexually mature males together. They will constantly fight with each other until one or both are dead.

Pro Tip: This doesn’t just go for Dempseys. This holds true for most of the big Central and South American cichlid species. In the wild, each male would stake out a territory and drive away any other male that came within sight.

Your only hope for having a community tank that includes Dempseys is to mix them with other species that have a similar adult size and aggression levels, like green terrors, firemouths or severums.

But you will need a big tank to pull this off, something like a 150 gallon (568 liter). If the Dempsey starts to feel crowded it will likely start killing other fish.

You should absolutely avoid smaller species of fish. Anything that a Dempsey can fit in its mouth will likely be made into a snack.

Even if the fish aren’t small enough to be eaten, it’s common for Jack Demsey fish to harass and kill smaller fish.

Diet Requirements and Feeding

Dempseys are primarily carnivores that hunt live prey in the wild. This means it’s important to provide them with a varied diet that is high in animal protein.

What can I feed my Jack Dempsey cichlid?

A high quality pelleted food should be the staple of your Dempsey’s diet.

I am particularly fond of Omega One Cichlid Pellets as well as Fluval Bug Bites Cichlid formula. Both foods provide lots of protein that comes from high quality sources.

The pellets are also big enough that they’re easy to feed to larger, adult fish.

In addition, it’s good to offer these fish a variety of live and frozen foods to round out their diet, like bloodworms, black worms, daphnia and brine shrimp.

Related: Best Cichlid Food

How often should I feed my Jack Dempsey cichlid?

You should feed juvenile Jack Dempseys 2-3 small meals each day to help them grow.

Adults should be fed 1-2 times a day.

It’s important not to overfeed, so only give them as much food as they will eat in about 2 minutes and immediately remove any uneaten food.

Is a Jack Dempsey Fish Right for You?

This is one of my all time favorite fish in the hobby. They’re big and fierce, with bright colors and great personalities.

But, they’re not for everyone.

It’s important that they have enough space since they are a fairly humongous fish. I really wouldn’t recommend putting a single Dempsey in anything under a 55 gallon, and that’s if it’s the only fish in the tank. 

If you want to keep a pair, or have other large cichlids in the tank, I’d recommend investing in at least a 100 gallon (378 liter) tank.

Since they are so big, they put off a lot of waste and require a strict maintenance schedule to keep their tanks clean and water healthy.

And it’s important to make sure you have enough filtration to keep up the large amount of waste this fish will produce.

These beautiful bruisers really aren’t good community fish. They can be aggressive and territorial. 

The only tank mates that stand a chance are other large Central American cichlids but be prepared to move or re-home fish if this doesn’t work out long term. 

If you can provide what they need, I highly recommend this fish. They’re absolutely gorgeous and make great pets.

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