Jack Dempsey Fish: 9 Basic Thing You Need to Know

We’re going to cover everything you need to know about the jack dempsey fish. This includes but is not limited to jack dempsey fish size, growth rate, lifespan, tank size, feeding, tankmates, overall behavior, aggression, breeding and egg laying.


Jack Dempsey Fish

What Are Jack Dempsey Fish?

The Jack Dempsey is a type of Central American cichlid. Their scientific name is ‎Cichlasoma octofasciatum. Their popular name is derived from a boxer who was famous in the 1920s.They’re sometimes called the Mexican blue fontosa. In the wild, these fish are found from Honduras to Mexico.


Why were these fish named after a boxer? It was in part because of their strong facial features, but a bigger factor was their aggressive nature. The aggression goes up when they are cramped, and you can reduce it by giving the fish plenty of caves and hiding places. Mated pairs will be more aggressive, especially when breeding. To minimize aggression, only add fish to the tank one at a time.

Proper Tank Mates

These fish can share a tank with other, similarly sized and equally aggressive North American cichlids. However, they have no issue eating much smaller fish. If it fits in their mouth, they’ll try to eat it.
When stressed, they’ll even eat their own offspring. Ironically, if you plan on having more than one Jack Dempsey cichlid, have multiple fish instead of a single pair to reduce aggression. A single species tank is ideal for this species.

Breeding and Egg Laying

These fish lay their eggs on hard, flat surfaces within their territory. This may be the glass bottom of the aquarium, a rock or a log. Both parents help incubate the eggs and guard the hatchlings. They’re good parents for fish, demonstrated by pre-chewing food for their offspring. However, if the breeding pair is disturbed or the environment becomes harsh, they may eat their fry.

These fish breed easily. They’ll breed readily in a well-kept tank. They lay eggs in protected places like caves; you can create one by putting a pot in the tank. These fish can lay several hundred eggs at a time. They’ll dig into the sand or small gravel until they reach the bottom of the tank, and then they’ll create a pit. They’ll transfer any fry that hatch into the pit to protect them.

When this happens, you will want to put in an aquarium divider to segregate the Jack Dempsey or simply remove all other fish from the tank to minimize aggression.

Their easy breeding in captivity means that you can find many farm raised fish.

Development and Growth Rates

As the Jack Dempsey matures, its coloring will change from light gray and tan with blue flecks to a grey with bright blue. Adult colors will change under stress, as well. In this case, their colors will become lighter and their spots less obvious. As they age, their colors will dim, too. Females have fewer spots than males in general. Only females will have a dark spot on the dorsal fin, but not all females have that.

There are several color variants available in the pet market, including gold, pink and electric blue. Males are a little bigger than the females, and they have brighter colors, as well. The largest specimens will reach 10” or 25 centimeters in length.

Life Span

These fish will regularly live ten to fifteen years. In some cases, they’ll live even longer.
These fish are prone to skin flukes, worms and other parasitic infections. Understand the signs of these diseases so that you can treat them early, since any infection can kill your Jack Dempsey cichlids.

Tank Size

These fish will grow to be anywhere from six inches (15 centimeters) to 10 inches (25 centimeters). When they have the space, they will typically reach a larger size. Give a single fish at least 55 gallons to give them space to grow and minimize aggression. If you have a breeding pair, 100 gallons is the minimum tank size. Growing fish could be kept in a 40 gallon tank for a while but need to be moved to a 50 gallon or larger tank when they approach their full size.

General Care

These fish are naturally found in warm, murky waters. They’re found in swamps, drainage ditches and sand-bottomed canals. Their ideal water pH is 6 to 7. They can handle water hardness between 9 dGH and 20 dGH. They’ll manage water temperatures from 72F to 86F, though normal water temperatures should max out at 82F. Their hardiness is why they are so popular with beginner aquarium owners.

These fish tend to swim in the middle to bottom of the tank. Give them a thick layer of sandy and small gravel substrate, because they like to burrow.

These fish are sensitive to variable pH and pollutants. This means that at least 20% of the tank water should be replaced biweekly, more if you have a densely populated tank. Take care to remove all of the decomposing organic matter in the gravel, because that is the source of problems for most tropical fish tanks.

They like moderate to normal lighting. There should be moderate water movement in the fish tank.
These fish can suffer from ich or white spot disease. Because of their broad temperature tolerance, you can treat that by raising the tank temperature to 86F for several days, assuming all the other fish in the tank can handle that.

They’re prone to head and lateral line erosion or hole in head disease. This can be treated by partial water changes, giving them proper nutrition and switching to biological water filtration in place of over-filtration with activated carbon.

Feeding Behavior

These fish are carnivorous, which helps to explain why they’re so aggressive. They will eat worms like glass worms, insects, crustaceans, and if small enough, other fish. They’ll try to eat shrimps, snails and crabs in your fish tank. They’ll eat freeze dried bloodworms and brine shrimp. They will take pellets and flakes; while mostly meat-eating, supplement with spirulina to give them a balanced diet. They’ll eat a lot of commercially prepared foods. They should be fed several times a day.

The Jack Dempsey fish will pick at and eat live plants. Because they’re not thrilled with direct lighting, you can put floating cover in the aquarium to diffuse the light and give them something to eat. You can reduce their tendency to pick apart your plants by giving them a little lettuce or blanched cucumber