Jack Dempsey

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: digs up plants.

Feeding

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.

Origin and habitat

Native to the Atlantic slope of Central America, from the Río Actopan in Veracruz, Mexico south through Belize and Guatemala to the Ulúa basin in Honduras. Inhabits swamps, muddy canals, drainage ditches, and slow-moving rivers with sandy or muddy bottoms; shows a preference for permanent pools with dense macrophyte cover. Named after the American heavyweight boxing champion Jack Dempsey (1895-1983), who held the title through much of the 1920s, for the fish's aggressive, combative temperament. The genus Rocio was erected by Schmitter-Soto in 2007; the name is Spanish for "morning dew" and also the first name of the author's wife, referencing the iridescent spots on the cheeks and flanks of member species. Octofasciata from Latin octo (eight) + fasciatus (banded), referring to the body pattern. Established invasive populations exist in the United States, Australia, Thailand, and Russia. A population was discovered in an isolated flooded quarry in New South Wales in 2004; three eradication attempts using explosives between 2004 and 2005 failed (NSW DPI). Males can reach up to 25 cm in captivity; some sources report a more typical range of 18-20 cm (Dallas World Aquarium). Females are smaller. Sexing is possible from a young age: females carry blue markings across the lower cheek and chin, while males show blue spots only behind the eyes and are unmarked on the lower face. Despite the aggressive reputation, they can appear quite shy, often hiding in caves and rockwork. The Electric Blue Jack Dempsey (EBJD) is generally considered a natural recessive color mutation isolated through selective breeding, though its exact origin remains debated; some hobbyists suspect possible hybrid ancestry. EBJDs are typically more docile, smaller, and more delicate than the standard form. Known color variants include gold, electric blue, and pink (a fish expressing both gold and blue traits).

Breeding

Substrate spawner with intense biparental care. The pair cleans a flat rock or digs a pit and the female deposits 500-800 eggs on the surface. Both parents guard the eggs aggressively. Eggs hatch in 2-5 days depending on temperature. Fry remain attached to the spawning site feeding off yolk sacs, then are moved to a pit by the parents and guarded until free-swimming, roughly a week after hatching. Parents may crush food and release it for the young. The parental defense is among the most vigorous of any aquarium cichlid; a breeding pair will attack anything that approaches regardless of size. New parents may consume their first few broods but usually improve with experience. Fry eat infusoria initially, then baby brine shrimp and microworms. 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

Further reading

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