Jack Dempsey

Quick facts

Adult size

25 cm

Lifespan

can live up to 15 years

Tank zone

mid-bottom

Temperament

aggressive

Difficulty

intermediate

Water parameters

Temperature

22–28°C

pH

6.5 to 8.0

Hardness

5 to 20 dGH

Tank requirements

Minimum volume

250 L

Minimum length

120 cm

Flow

low

Lighting

dim preferred

Substrate

sand

Driftwood

preferred

Hiding spots

needed

Open swimming room

needed

Feeding

Diet: carnivore, feeds primarily at the mid-bottom.

Carnivore-leaning omnivore. Pellets (cichlid pellets, not community food), frozen krill, frozen shrimp, frozen bloodworm, frozen silversides, and live earthworms. Will eat vegetable matter but doesn't seek it out. Feed once or twice daily. Adults are messy eaters that produce a lot of waste; strong filtration is essential. Live food triggers hunting behavior and keeps the fish mentally stimulated.

Compatibility

• Named after the boxer for a reason. Jack Dempseys are pugnacious, territorial, and will fight other cichlids for dominance. They're not mindlessly aggressive (they won't chase neon tetras around the tank), but they won't share territory with similar-sized or similar-shaped fish.
• Tankmates need to be tough, fast, or large enough to hold their own: silver dollars, large catfish (raphael, pleco), large loaches, and other robust Central American cichlids (firemouths, severums). Avoid anything delicate, slow, or similar in shape to another cichlid.
• A bonded pair is aggressive enough to clear a 300-liter tank of all other fish during breeding. If keeping a breeding pair in a community, the tank needs to be large (400 L) with distinct zones.
• The "electric blue" Jack Dempsey variant is smaller, less aggressive, and more fragile than the standard form. It's effectively a different fish in terms of temperament despite being the same species.

Habitat

Native to Central America: Mexico (Yucatan Peninsula), Belize, Guatemala, and Honduras. Found in slow-moving rivers, lakes, and cenotes with sandy or rocky substrates. Also established as an invasive species in parts of the southern United States and Australia through aquarium releases. Adults reach 20–25 cm in aquariums, occasionally larger. The body is deep, stocky, and covered in iridescent blue-green spangles that become more intense with age and good diet. Males develop a pronounced nuchal hump (forehead bump) and are larger than females. The species has been in the hobby since the 1920s and remains popular despite (or because of) its aggressive personality. The electric blue Jack Dempsey, a recessive color variant with all-over metallic blue coloring, appeared in the 1980s from a South American breeder and is now widely available. Standard Jack Dempseys are bred commercially; wild-caught specimens are uncommon in the trade.

Breeding

Substrate spawner with intense biparental care. The pair cleans a flat rock or digs a pit and the female deposits 500-800 eggs. Both parents guard the eggs and fry aggressively, attacking anything that approaches regardless of size. Eggs hatch in 3-4 days. Fry are herded in a tight cloud by the parents for 4-6 weeks. The parental defense is among the most vigorous of any aquarium cichlid; a breeding pair of Jack Dempseys in a community tank will disrupt the entire social structure. Fry eat baby brine shrimp and crushed pellets. Breeding isn't difficult; the challenge is managing the aggression of the parents during brood care. A dedicated breeding tank of 200 L is the practical approach.

Common problems

Aggression management is the main challenge. A single Jack Dempsey in an appropriately sized tank (250 L) is manageable. A pair during breeding is a project. Two males is a fight. Tank size is frequently underestimated because juveniles are sold at 5–8 cm and reach 20 cm within a year. Hexamita (hole-in-the-head) is the signature disease for Central American cichlids, caused by a combination of Hexamita parasites, poor diet, and suboptimal water quality. Prevention: varied diet with occasional vegetable matter, clean water, and low nitrate. Treat active infections with metronidazole. The electric blue variant is significantly more delicate than the standard form: it grows slower, stays smaller, is more susceptible to disease, and is less aggressive. Treat the two forms as different fish for stocking purposes.

Bioload

Bioload coefficient: 8.0 (large aggressive cichlid; heavy feeder, heavy waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size