Jack Dempsey care guide
Also called: Jack Dempsey cichlid, Jack Dempsey fish, Electric blue Jack Dempsey, Cichlasoma octofasciatum
The Jack Dempsey is a tough, aggressive Central American cichlid covered in glittering blue-green spots. It grows to about 8 inches (20 cm), so one needs at least 55 gallons (208 L) with caves, and its tankmates must be large and robust.
Jack Dempseys need a tank of at least 55 gallons (208 L), and water at 22–28°C (72–82°F) with a pH of 6.5–8. They grow to about 20 cm (7.9 in) and are aggressive.
Plan a tank with Jack DempseysSee all tank mates
Jack Dempsey quick facts
| Scientific name | Rocio octofasciata |
|---|---|
| Family | Cichlidae |
| Origin | Atlantic slope of Central America, from southern Mexico to Honduras (most sold are captive-bred) |
| Adult size | 20 cm (7.9 in) |
| Minimum tank | 55 gallons (208 L), at least 120 cm (47 in) long |
| Temperature | 22–28°C (72–82°F) |
| pH | 6.5–8 |
| Hardness (GH) | 8–20 dGH |
| Group size | Alone or as a pair |
| Temperament | Aggressive; males fight each other |
| Swims at | Bottom |
| Diet | Omnivore |
| Care level | Moderate |
| Lifespan | 8–15 years |
| Safe with shrimp? | No, eats shrimp |
| Safe with plants? | No, eats or uproots plants |
Tank setup
One adult needs at least a 55-gallon (208 L) tank 4 ft (120 cm) long. A pair or a mixed cichlid tank needs 75 gallons (284 L) or more, ideally 5 ft (150 cm) long. Build several caves and sight barriers from rock and wood so each fish can claim a space. It digs, so use sand or fine gravel and choose plants that float or grow on decor.
How many Jack Dempseys in a tank?
The smallest common tank that suits Jack Dempseys is a 55 gallon. Here is roughly how many fit in each size when they are the only fish, based on adult size and waste output. Leave room if you want tank mates.
| Tank | Jack Dempseys (alone) |
|---|---|
| 3 gallon | Too small |
| 5 gallon | Too small |
| 10 gallon | Too small |
| 15 gallon | Too small |
| 20 gallon | Too small |
| 20 gallon long | Too small |
| 29 gallon | Too small |
| 40 gallon | Too small |
| 55 gallon | Up to 3 |
| 75 gallon | Up to 4 |
| 125 gallon | Up to 7 |
Numbers are bioload limits only. Males fight, so keep one fish or one pair.
What you need for Jack Dempseys
Sized for a 55 gallon tank, the smallest common size that suits Jack Dempseys. For a different tank or a mix of fish, use the stocking calculator for a list sized to your plan.
Tank and equipment
- 55 gallon aquarium (tank or kit) (opens Amazon in a new tab)Bigger tanks are more stable and easier for beginners. How to choose
- Aquarium stand for 55 gallons (opens Amazon in a new tab)The water alone weighs about 459 lb (208 kg), before glass, gravel and rock. How to choose
- 2 adjustable heaters, 100 W each (opens Amazon in a new tab)Holds about 77 °F (25 °C) in a room at 65 °F (18 °C). Two heaters keep the tank warm if one fails. How to choose
- Aquarium thermometer (opens Amazon in a new tab)Check it daily: heaters can fail stuck on or off. How to choose
- Canister filter rated 330–550 GPH (opens Amazon in a new tab)Heavily stocked or messy fish: 6–10 times the tank volume per hour. How to choose
- About 75 lb of aquarium gravel (opens Amazon in a new tab)Enough for a layer about 2 in (5 cm) deep. Smooth gravel suits most community fish. How to choose
- Water conditioner (dechlorinator) (opens Amazon in a new tab)Removes chlorine and chloramine from tap water. Seachem Prime is a popular, concentrated choice. How to choose
- Liquid test kit (ammonia, nitrite, nitrate, pH) (opens Amazon in a new tab)Liquid kits are more accurate than strips. The API Freshwater Master Test Kit is the common choice. How to choose
- Gravel vacuum (siphon) (opens Amazon in a new tab)Cleans the gravel and does the water change in one go. How to choose
- LED aquarium light, about 48 in long (opens Amazon in a new tab)Match the light to the tank length. Basic LEDs grow easy plants. How to choose
Food and extras for Jack Dempseys
- Sinking pellets or wafers (opens Amazon in a new tab)Bottom feeders need food that reaches the floor.
- Caves and hides (opens Amazon in a new tab)Gives shy and territorial fish their own space.
Product links go to Amazon search results. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Disclosure.
Water parameters
Keep it at 22–28°C (72–82°F), pH 6.5–8.0 and moderately hard water. It is hardy and copes with most tap water, but its heavy waste calls for strong filtration and 30% water changes every week. Subdued lighting helps new fish settle in.
Best tank mates for Jack Dempseys
These popular species share Jack Dempseys' water needs and temperament. See the full list of 3 good matches.
Oscar
30 cm (11.8 in) · 23–27°C (73–81°F)
Jewel cichlid
10 cm (3.9 in) · 24–27°C (75–81°F)
Green terror
20 cm (7.9 in) · 20–24°C (68–75°F)
Avoid keeping Jack Dempseys with
- Bristlenose pleco: Jack Dempsey is aggressive and will bully or injure peaceful bristlenose plecos.
- Bronze corydoras: Jack Dempsey is aggressive and will bully or injure peaceful bronze corydoras.
- Cherry shrimp: Jack Dempsey eats small shrimp like cherry shrimp.
- Common goldfish: Jack Dempsey is aggressive and will bully or injure peaceful common goldfish.
- Common pleco: Jack Dempsey is aggressive and will bully or injure peaceful common plecos.
- Dwarf gourami: Jack Dempsey is aggressive and will bully or injure peaceful dwarf gouramis.
Feeding
A meat-leaning omnivore. Feed a quality sinking cichlid pellet as the staple, plus frozen bloodworms, mysis, krill and chopped prawn. Earthworms and insects make good treats. Add a spirulina- or vegetable-based food now and then.
Behavior
Aggressive and territorial, most of all toward its own kind and similar-shaped cichlids. It eats fish that fit in its mouth and hunts shrimp and snails. Tankmates should be robust and close to its size, such as large plecos, silver dollars, severums and other sturdy cichlids in a big tank. The electric blue Jack Dempsey stays smaller and is often milder, but needs the same care.
Breeding
Pairs form readily from young fish and stay together. They clean a flat stone or the floor of a cave, often digging a pit nearby, and the female lays several hundred eggs. Both parents guard the eggs and fry fiercely. A male may attack a female that isn't ready, so watch new pairs closely and keep a divider handy.
Tips from experienced keepers
- Add all your cichlids at the same time, as juveniles, so no single fish claims the whole tank.
- Give every fish its own cave, plus a spare or two. Fighting drops when everyone has a retreat.
- Don't mix it with peaceful community fish like tetras, gouramis or corydoras.
- Pick tankmates with a different shape and color, like a severum. Look-alike cichlids get attacked more.
- A breeding pair spawns again and again. Have a plan for the fry before you keep a pair.
Frequently asked questions
Are Jack Dempseys aggressive?
Yes. They are territorial cichlids that fight their own kind and bully smaller or timid fish. A large tank with plenty of caves keeps aggression down.
How big do Jack Dempseys get?
In home aquariums, males usually reach about 8 inches (20 cm) and females about 6 inches (15 cm). The electric blue form stays smaller.
What size tank does a Jack Dempsey need?
At least 55 gallons (208 L) for one adult, and 75 gallons (284 L) or more for a pair or a mixed cichlid tank.
Sources
We checked these references when writing this page. Values are for healthy long-term keeping, not survival limits. Last reviewed 2026-10-13. See our editorial policy.