Jack Dempsey Fish


Jack Dempsey fish overview

The Jack Dempsey fish is one of the most popular freshwater aquarium fish. They’re in the cichlid family which includes over 1,500 species including angelfish, African cichlids and discus. Jacks are named after world heavyweight boxing champion (1919-1926) Jack Dempsey. Nicknamed the “Manassa Mauler”, Jack Dempsey was famous for his ruthless, unbridled attacks in the boxing ring. Likewise, Jack Dempsey cichlids can be very aggressive toward other fish in the aquarium. Even so, the Dempsey’s interesting personality and beautiful coloration are a favorite among cichlid enthusiasts. Here’s what you need to know about keeping Jack Dempsey’s in your aquarium.

Jack Dempsey Fish

Natural habitat

Jack Dempsey Fish Natural Habitat

The original wild Jack Dempsey fish, currently classified as Rocio octofasciata, is a native to Mexico (Papaloapán River), the Yucatan, Honduras (Ulua River) and Guatemala. The fish can be found thriving in a variety of environments other tropical fish could not survive. It is common for populations of R. octofasciata to live in shallow, slow-moving streams, irrigation ditches and weedy bog zones. The hot water (72–86 °F) and lower oxygen conditions are a testament to the hardiness of the Jack Dempsey. The fish are also found in rivers but they tend to remain in areas of slower water movement like natural caves, near rocks and submerged branches. Biologists have discovered non-native populations of Dempseys in North America, mainly around tropical fish farms in Florida. The cichlids are probably escapees from the fish farms. Single fish have even been found in South Dakota, Hawaii and Connecticut. Jack Dempsey fish have also been found living in Thailand and Australia. These fish are believed to have been released into the wild by aquarists.

Jack Dempsey Fish Varieties

Jack Dempsey Fish

The wild type Jack Dempsey starts out as a somewhat plain juvenile with relatively muted grayish-tan colors. Young fish display ten to twelve pale vertical strips. These fade as the fish grows into the adult stage. Traces of iridescent turquoise scales are a hint of the color development as the fish matures. The body shape is called “laterally compressed.” This is a fancy term that means the fish looks thin when you look at it face to face. This body shape is common to a many of the carnivorous, predatory fish species. If you happen to be prey, the thin build of the Jack Dempsey is hard to see. But the muscular fish is very fast. The streamlined shape allows the fish to dart out of a cave or from under a log and gulp down an unsuspecting fish. As the Dempsey matures, the beautiful colors really start to come out. The main background color is dark blue, almost black. Iridescent blue and green scales create a beautiful pattern along the sides of the fish. The gill cover (operculum) also has the blue and green pattern. Jack Dempsey fish have lighter, bluish-colored lips that really give the fish personality. The tips of the dorsal fin are colored red. Females appear similar to the males. Some aquarists say the females are smaller and appear a bit paler in color. The Electric Blue Jack Dempsey fish variety is a bit smaller than regular Jack Dempseys but has an iridescent “electric blue” color. This variety is thought to be either a morph of wild types developed through selective breeding. The Electric Blue Jack Dempsey variety is known to be less aggressive nature compared to standard Jack Dempsey fish.

Aquarium requirements

Jack Dempsey fish are frequently sold as juveniles, measuring 2 to 3 inches in length. The young fish are often “packed” into a display tank at the aquarium shop. This leads novice aquarists to believe the fish will stay relatively small and live happily in a 10 or 20 gallon aquarium. The truth is, the Jack Dempsey will quickly outgrow a small fish tank. If you’re going to keep one or more of these fish, it is best to set up an aquarium dedicated to the needs of your Jack Dempsey fish. Since the fish will grow to a length of 10 inches, a 55-gallon or larger aquarium is recommended. These big fish need room to swim and explore. They are territorial and will act more aggressively when too many fish are kept in the same tank. Two or three mature Dempseys should be quite happy in a 55- to 150-gallon aquarium. But there’s more than aquarium size to consider when keeping large cichlids like Jack Dempsey fish. Here is a breakdown of all the important parameters and aquarium hardware needed to keep your Jack Dempsey healthy and happy.

Water Chemistry Conditions

Unlike some tropical fish, Jack Dempseys thrive in a wide range of water chemistry parameters. The fish can be kept in a pH range of 6.5 to 8.0. Water hardness and alkalinity (carbonate hardness) are not critical. A range of 5 to 12 degrees is acceptable to the Jack Dempsey fish. If your water has low alkalinity, the pH may tend to drop to the acidic pH range over time. Alkalinity stabilizes pH. Natural acids produced by the break-down of fish waste and biological filtration neutralizes alkalinity. If the alkalinity drops to less than 3 degrees, the pH could suddenly drop below pH 6.0. Test pH and alkalinity every week or two to keep a close watch on these important water chemistry parameters. Water changes, made every three to four weeks, will usually replenish alkalinity and stabilize the pH. Set the aquarium heater to maintain a water temperature of 78 to 82°F. An aquarium thermometer is helpful for making sure the heater is keeping the water temperature at the desired set point. Ammonia and nitrite must always be zero. Even low levels of these pollutants will stress your fish. Chronic exposure to ammonia or nitrite will weaken the fish’s immune system, leading to many disease problems.

pH:6.5 – 8.0
General or Total hardness:5 – 12 degrees
Alkalinity or carbonate hardness:5 – 12 degrees
Water temperature:78 – 82°F (25 – 28°C)
Ammonia & Nitrite:0.0

Water filtration

Large cichlids, like Jack Dempsey fish, produce a lot of solid waste. Unlike small tropical fish, Jack Dempsey waste is quite large and visible in the aquarium. You’ll want a powerful filter capable to suspending waste particles and filtering them out of the water. Since Dempseys require a big aquarium, be sure not to skimp on the filter system. Aquarists usually select a large hand-on-back (HOB) power filter or a canister filter. Most aquarium filters are rated based on aquarium size. Tank-handling figures are often exaggerated. It’s a good idea to select the next largest size aquarium filter, especially for a big aquarium containing big fish. HOB power filters with multiple cartridges are easy to clean. They should also contain activated carbon to remove odors and adsorb dissolved organics. A canister filter will hold more mechanical filter media like filter sponges. Mechanical filter media traps and hold solid particles, helping the water stay clear. No matter what type of filter you choose, be sure to service it once a month. Aquarium filters are designed to allow water to bypass the filter media if it becomes clogged. This safety feature ensures the filter still pumps water, even if the media are clogged with debris. The downside is that the organic “muck” will decompose inside the filter if not cleaned out frequently. Decomposing organic matter releases algae-promoting nutrients into the water, stimulating green water blooms and growth on the glass, gravel and ornaments.

Electric Blue Jack Dempsey

Aquarium lighting

A properly illuminated tank creates the appearance of deep water and brings out the color of your Jack Dempsey fish. Fluorescent lighting is the standard light style for aquariums, but LED lighting fixtures are quickly becoming the favorite fixture for aquarium lighting. Here’s why. Most fluorescent aquarium bulbs are designed to highlight the artificial “Day-Glo” colors of aquarium gravel, plastic plants and ornaments. That’s great if that’s the look you’re going for. But the natural colors of tropical fish are often lost in this artificial light. Natural “daylight” fluorescent light bulbs are available as a retrofit, making it easier to grow plants and create a more natural-looking aquarium. However, the light quality of fluorescent bulbs begins degrading as soon as they are turned on. The lights will gradually dim and the color shift over a period of 9-12 months. The bulbs require replacement to maintain the same level of illumination. LED lighting uses much less energy and lasts for many years. Basic LED aquarium fixtures will provide natural-looking light and very low energy consumption. Some fixtures even have a built-in timer. The next level of light fixture has more LEDS for better light coverage, especially in deep aquariums. Some models even allow you to custom-tailor the light color to highlight the fish’s colors and create a gradual sunrise and sunset lighting program.

Aquascaping for Jack Dempsey fish

Like many cichlids, Jack Dempsey fish have a natural instinct to dig in the aquarium substrate. If you watch closely, you’ll notice they “sift” the gravel, looking for food like crustaceans and worms. You can use any size gravel but the ideal substrate is fine sand. The sand is easier for the fish to sift and explore, satisfying their natural urge to dig around the aquarium. The other benefit to using sand is that sand settles and levels itself after being sifted. Larger aquarium gravel tends to get “bulldozed” into piles, leaving craters around the aquarium. The fish like rocks and crevices to hide in and explore. Driftwood or resin logs and branches provide much appreciated cover and territory for the fish. Hardy live plants like Anubias and java moss can be grown in a Jack Dempsey fish aquarium. Taller Vallisneria also provides dense cover for the fish to swim through.


Jack Dempseys will eat a variety of prepared, fresh, frozen and live foods. They’re carnivorous and will eat just about any fish that will fit in their mouth. If you’re into feeding live foods, the fish will eat small fish, worms and even brine shrimp. Pieces of frozen mysis shrimp, brine or bloodworms are also a favorite treat. Prepared cichlid or carnivore pellets are the most popular diet for large cichlids like Dempseys. Floating and sinking pellets are readily accepted. Feed only what the fish will consume in a minute or two. Never let the uneaten food float or sit at the bottom of the tank after feeding time. The food will decay and pollute the water.


Jack Dempsey fish’s experts suggest raising small fish together and waiting for a pair to separate from the group. This ensures compatibility and reduces the chances of fighting during courtship. Be aware that during courtship and pairing, all other fish in the aquarium will be driven away, bullied or even killed. Be prepared to remove the fish before this happens. The female Dempsey must be ready to spawn. If not, the male may chase and bully her. Be ready to remove or separate the female if things get rough. Give the pair a flat stone to use for spawning. They will pick at the stone, cleaning it in preparation for egg laying. After the female lays eggs on the stone, the male will fertilize them. Both parents watch over the eggs. Once the eggs hatch (3 days), they are collected by the parents and dropped into “pits” dug into the aquarium gravel. The fry become free-swimming in about 10 days. The young fish will eat frozen baby brine shrimp and small bits of prepared food.

Final thoughts

The Jack Dempsey fish can live up to 10 years with proper care. The key to a long life in an aquarium is good water quality and a healthy diet. Important thing is a stable water conditions, so self cleaning fish tank would be a good choice, free of ammonia and nitrite, are critical for the health of the fish. A build-up of sludge in the aquarium, common with large fish, can become a breeding ground for disease causing organisms. Use a gravel siphon to keep the substrate clean. Change 15 to 20% of the aquarium water every month. Over-feeding will pollute the aquarium and cause the fish to become obese and unhealthy. Follow these guidelines and your fish will reward you with beautiful colors and interesting behavior for years to come!

Jack Dempsey Natural Habitat