Back when I first started keeping fish, I was drawn to species that acted like they had a bit of personality. The Jack Dempsey? That fish has more attitude than most people I know. Named after the boxer because of its aggressive nature and scrappy behavior, it’s a freshwater fish that doesn’t mess around. If you’re into bold fish with color, strength, and a little swagger, the Jack Dempsey is your guy.

This guide lays out what you need to know — from how to care for them to what they eat and why they sometimes go after their tankmates. This isn’t your average passive aquarium pet. It’s a true brawler with flair.

What is a Jack Dempsey Fish?

The Jack Dempsey is a cichlid native to Central America, often found in slow-moving rivers with muddy bottoms. These fish can grow up to 10 inches in the wild, though they usually cap out around 8 inches in a home tank.

• Scientific Name: Rocio octofasciata
• Origin: Mexico, Honduras, Guatemala, and Belize
• Water type: Freshwater, warm temperature range
• Adult Size: 6 to 10 inches

The fish gets its name from the 1920s heavyweight boxing champ Jack Dempsey, and once you see how they act in a tank, you’ll understand why.

Behavior and Temperament

Jack Dempseys are aggressive and territorial, especially when they’re guarding eggs or if the tank is too small. These fish are smart and will establish dominance in their space. I’ve seen them pick fights with fish twice their size, just to show who’s boss.

• Very territorial: They don’t tolerate many intrusions
• May dig up substrate: Often rearrange the tank decor
• Smart and responsive: Recognize their owners and will interact
• Better solo or with equally tough fish: No guppies in here

If you’re planning to keep one, give them space and don’t crowd the tank. If you’re housing multiples, expect some fights unless the tank is large with lots of hiding places.

Tank Setup

I recommend at least a 55-gallon tank for one adult Jack Dempsey. If you want more than one or you’re thinking of adding tankmates, go bigger. Water needs to stay warm and clean. These fish like it stable — not too many spikes or sudden changes.

• Minimum tank size: 55 gallons for one fish
• Ideal temperature: 75 to 82°F
• pH range: 6.5 to 8.0
• Substrate: Sand or smooth gravel
• Filtration: Strong filter, they’re messy eaters

Keep rocks, driftwood, and hiding spots in the tank. They like places to claim as their own. Don’t use sharp decor though — they tend to charge around and you don’t want them getting injured.

Feeding the Jack Dempsey

Jack Dempseys are carnivores but will eat a mix of food. I give mine a rotation of pellets, frozen foods, and the occasional live treat. A good diet brings out their color and keeps them aggressive in the right way — healthy, not erratic.

Feeding Chart

Tank Mates: What Works and What Doesn’t

This is where most people go wrong. You can’t toss a Jack Dempsey into a community tank and expect peace. They do best with fish that can hold their own. Avoid anything small, slow, or delicate.

• Good tank mates: Convict cichlids, Firemouths, Green Terrors, Plecos
• Risky choices: Oscars (depends on space and personality)
• Bad ideas: Tetras, guppies, goldfish, anything peaceful or fragile

If you’re trying a mixed tank, add all fish while young and let them grow together. That sometimes helps, but there’s no guarantee. Always keep an eye out for injuries or signs of stress.

Breeding Jack Dempseys

Breeding these fish is doable if you have the right setup. I’ve bred them in 75-gallon tanks with a bonded pair. They dig pits, lay eggs, and then fiercely protect them. Don’t even think about reaching in once eggs are laid unless you want to get bit.

• Bonded pair needed: Not all male/female combos work
• Spawning site: Smooth rock or flat surface
• Egg count: 300 to 500 eggs per spawn
• Parental care: Both parents guard the eggs and fry

If you want to raise the fry, move them to a separate tank once they’re free-swimming. Parents can get aggressive, even with their own kids once the breeding instinct fades.

Final Thoughts

Jack Dempsey fish are bold, beautiful, and full of personality. They aren’t for everyone — especially not beginners — but if you’ve got the space and know what you’re doing, they’re one of the most rewarding fish you can keep. They’ll interact with you, hold their ground, and display color like nothing else when they’re in top shape.

Just give them room, give them food, and give them respect. You won’t regret it.