Should I buy it?
Jack Dempsey
Rocio octofasciata
Also known as: j.d., rio grande cichlid
Robust New World cichlid that develops electric blue spotting as it matures. But aggressive, large, and not community-safe.
Jack Dempsey tank mates · 200L tank size hub
aggressive · intermediate care
Sources & confidencehigh · partially verified · beginner: not recommended
Checked against several solid care sources that mostly agree. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Single-species or paired-cichlid setups of 300 L or more with serious filtration and rockwork.
Avoid if: You wanted a community fish, your tank is under 250L, or you can't manage cichlid aggression.
Common mistakeBuying two Jack Dempseys ‘for company’ in 200L is how keepers invent a permanently cornered fish. Even a matched pair needs divided territory and honest footprint. Do not park a juvenile in a neon community hoping adulthood will stay peaceful — mouth size and temper arrive together.
Top things that go wrong
- Grows large or needs a very big footprint. Jack Dempsey is often sold at sizes that hide adult length (~25cm) and a published minimum near **200L**. Shop tanks are not adult housing.
- Mouth gap vs tiny tank mates. May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
- Shrimp & snails. Not shrimp-safe — adults, fry, or both get eaten.
What most shops don't tell you
- 1.Myth: juvenile Jack Dempseys stay manageable community cichlids if they grow up with their tank mates. Reality: adults are territorial predators — ‘they grew up together’ is a schedule, not a law, and nano fish disappear when the mouth catches up.
- 2.Predation risk scales with gape, night feeding, and crowding. 'they grew up together' is a schedule, not a law.
- 3.Buying for juvenile size in the shop tank. Budget for adult length and turning radius, not the inch-long fish in the bag.
- 4.Adding bite-sized tetras or livebearers "until the predator grows". The first lost fish lands months earlier than the plan said.
- 5.Not suitable for community tanks. Keep only with similar-sized aggressive cichlids or alone. Requires a large tank with hiding spots and robust decor.
About this species
Jack Dempseys are 20 to 25 cm Central American cichlids named for the boxer. Adults develop iridescent blue-green spotting and defend a territory hard, especially when breeding.
- African Cichlid200L min · same group, comparable tank size
- Convict cichlid200L min · same group, comparable tank size
- Discus200L min · same group, comparable tank size
- Firemouth Cichlid200L min · same group, comparable tank size
- Keyhole cichlid200L min · same group, comparable tank size
- Rainbow cichlid200L min · same group, comparable tank size
- Electric Blue Acara150L min · same fish family
- Severum250L min · same fish family
- African Cichlidalso intermediate aggressive, similar tank size
- Green Terroralso intermediate aggressive, similar tank size
- Oscaralso intermediate aggressive, similar tank size
- Common Pleco tank matesnames this fish as a conditional pairing — read the pair page conditions
- Green Terror tank mateslists this fish as a safe and recommended mate
- Oscar tank mateslists this fish as a safe and recommended mate
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease26
- Peacefulness0
- Community fit0
- Small-tank fit80
- Hardiness54
- Energy54
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Avoid “one of everything” baskets — Jack Dempsey belongs in a plan built around territory, line-of-sight breaks, and matched water chemistry.
Compatibility
Tank mates for Jack Dempsey
Usually safer (engine GOOD): Green Terror, Oscar. Conditional (CAUTION — read the pair page before buying): Angelfish, Common Pleco. Avoid (RISKY): Corydoras Catfish, Guppy, Neon Tetra, Tiger Barb. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Jack Dempsey + Green Terror
- Try Green Terror — open the pair check.
- Try Oscar — open the pair check.
Behaviour and temperament
Jack Dempseys are aggressive and territorial. They can look calm for hours, then rearrange the tank and punish weaker fish. Pair them with their own kind only with serious planning, or keep similarly robust Central American cichlids — never a mixed tetra community as a long-term plan.
What sets them off
- Crowding and limited territory
- Similar-looking fish in the same tank
- Spawning, for any breeding pair
Fin nipping: Not a habitual fin-nipper; stressed or crowded individuals can still test fins.
Predation: May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
Territory: Holds a patch (cave, corner, or surface). Break sight lines so neighbours can pass.
Planted tanks: caution — pick tougher plants
In the glass: typical and warning signs
- An adult holds mid-to-bottom territory and flares at reflections and rivals.
- Digging and rearranging hardscape are normal large-cichlid ownership.
- A subordinate fish pinned in a corner needs separation the same day appetite collapses.
- Constant glass pacing in a short tank means footprint failure before mystery disease.
- Sudden attacks on smaller fish are ownership math, not a one-off bad mood.
- Two adults without room will fight until one is injured or starved.
- Remove nano and peaceful community fish before adult size arrives — do not wait for the first disappearance.
- Divide or rehome when a pair fight cannot be broken with hardscape alone.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
variable
Diet
carnivore
Jack Dempseys are large carnivores that clear meaty foods and cichlid pellets in serious quantities. A tetra-sized pinch leaves them scavenging décor and tank mates. Feed by appetite with frozen foods and quality pellets, and expect bioload to match a 200L-class filtration plan — not a community flake schedule.
Shrimp & snails
Not shrimp-safe — adults, fry, or both get eaten.
Jack Dempsey is fine singly or as a researched pair — check behaviour before doubling up.
- Hold 22 to 28 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 6.5 to 8 and a hardness you can re-test in two weeks. A one-time strip in the shop car park is not a water test.
- Footprint: short wide tanks and tall narrow tanks fish differently for the same volume. Match the tank shape to the swim pattern, not just the litre count.
- Tank volume meets or exceeds 200L published minimum for adults.
- Heater can hold 22–28°C without cooking cooler-water tank mates.
- No tank mates small enough to fit the adult mouth gap for this species.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 200L minimum tank needs a filter rated for at least 800L/hr turnover and a heater to hold 22–28°C reliably.
Research: partially verified · Confidence: high · 3 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- Seriously Fish. Rocio octofasciata
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Rocio octofasciata
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Rocio octofasciata
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
Evidence notes
- The Seriously Fish profile for the binomial in this record was successfully reached as the primary aquarium reference.
- FishBase contributes natural-range size and habitat context. Translate those numbers through your heater, your water report, and your tank footprint before stocking.
- Wikipedia is only cited if the article URL returned OK. Use it for orientation, not as the only care sheet for an import.
- All compatibility text reflects typical hobby experience and the Fishori model. Individual fish, shop stress, and the order tank mates are added in can still defy a single-paragraph label.
Featured compatibility checks
Curated pair pages for Jack Dempsey. Each opens a full verdict — not just a list label.
Common questions about Jack Dempsey
- How big do Jack Dempsey get?
- 20 to 25 cm for a male; females slightly smaller. Adult JDs need real volume. They do not stop growing in a small tank. They just become stressed.
- What size tank does Jack Dempsey need?
- 300 L absolute minimum for one. 450 L or more for a bonded pair.
- Are Jack Dempsey aggressive?
- Jack Dempseys are aggressive and territorial. They can look calm for hours, then rearrange the tank and punish weaker fish. Pair them with their own kind only with serious planning, or keep similarly robust Central American cichlids — never a mixed tetra community as a long-term plan.
- What is the most common mistake with Jack Dempsey?
- Buying two Jack Dempseys ‘for company’ in 200L is how keepers invent a permanently cornered fish. Even a matched pair needs divided territory and honest footprint. Do not park a juvenile in a neon community hoping adulthood will stay peaceful — mouth size and temper arrive together.
- What fish can live with Jack Dempsey?
- The Jack Dempsey profile lists Green Terror, Oscar among its safer pairings (engine-checked GOOD). Angelfish, Common Pleco are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid Corydoras Catfish, Guppy, Neon Tetra, Tiger Barb (RISKY). Run the pair checker for your exact water and tank size before stocking.