Should I buy it?
Rainbow / red-tailed black shark
Epalzeorhynchos frenatum
Also known as: rainbow shark, ruby shark, red-tailed black shark (fish. Not a true shark)
Dark body with bright red fins, bottom zone. Calm as a juvenile, then territorial as it matures, and will fight other rainbow sharks to the death.
Rainbow / red-tailed black shark tank mates · 200L tank size hub
semi-aggressive · intermediate care
Sources & confidencehigh · partially verified · beginner: caution
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: Community tanks of 150 L or more where a single rainbow shark holds its own territory and rockwork.
Avoid if: Your tank is small, you want two rainbow sharks together, or you keep slow long-finned fish.
Common mistakeBuying two rainbow sharks for a large community is how keepers invent a fight until one is torn and injured. One per tank, regardless of litres, is the honest rule for adults. Cute juveniles become territorial fish that punish other sharks and similar bottom shapes without mercy.
Top things that go wrong
- Fin-nipping risk in typical community layouts. Will nip long fins or slow fish when the school is too small, bored, or kept in a short tank.
- Shrimp & snails. Shrimp are a gamble with this fish; some ignore them, some clear a colony in days.
What most shops don't tell you
- 1.Myth: rainbow sharks stay peaceful if you keep two together in a big enough community tank with caves. Reality: two adults fight for the bottom territory — keep one per tank, with length and robust tank mates, not a shark duo for company.
- 2.Spawning, breeding, or rearranging territory can make normally calm fish surprisingly aggressive in short tanks or with rival shapes.
- 3.Large minimum volumes still need real footprint: length and width for turning matter as much as the litre number on a sticker.
- 4.Fin nipping can appear when the group is too small, the tank is too short, or fish are bored. Fix structure and numbers, not just water changes.
- 5.Multiple 'sharks' in 120 L, leading to chronic chasing and tattered fins.
- 6.Housed with red-tailed black shark lookalikes in the same territory band without the footprint to separate them.
- 7.Nippy when the tank is short or thin on structure. Keep one per community; multiple rainbow sharks only in long feature-rich systems with redundant territories.
About this species
Rainbow sharks are dark-bodied cyprinids with a bright red tail and a strong bottom territory in the tank. Adults chase fish of a similar shape, more so in short tanks. They need line-of-sight breaks in hardscape, real tank length, and careful pairing.
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- Apistogramma Macmasterialso intermediate semi-aggressive, similar tank size
- Banded leporinusalso intermediate semi-aggressive, similar tank size
- Cockatoo / crested Apistogrammaalso intermediate semi-aggressive, similar tank size
- Electric Blue Acaraalso intermediate semi-aggressive, similar tank size
- Firemouth Cichlidalso intermediate semi-aggressive, similar tank size
No reverse lookups listed yet.
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 ease32
- Peacefulness22
- Community fit0
- Small-tank fit90
- Hardiness54
- Energy86
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 — Rainbow / red-tailed black shark belongs in a plan built around territory, line-of-sight breaks, and matched water chemistry.
Compatibility
Tank mates for Rainbow / red-tailed black shark
No unconditional “safe” tank mates are listed for Rainbow / red-tailed black shark — every listed candidate is a conditional pair check, not a green light. Conditional (CAUTION — read the pair page before buying): Angelfish, Bala / silver shark, Betta, Boesemani Rainbowfish, Chili Rasbora. 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.
None listed. Use the pair checker before mixing.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
None listed. Use the pair checker before mixing.
No safe-mate list on this record yet. Use the fish index to find species with similar care, then run a pair check before you buy.
Behaviour and temperament
Rainbow sharks are semi-aggressive and territorial bottom claimants. Calm as juveniles, nastier as mature adults, especially toward other sharks and similar bottom fish. Stress and injury explode when two share a tank or the footprint is too short for patrols.
What sets them off
- Small groups or boredom
- Long-finned or slow tank mates
- Bare tanks without structure
Fin nipping: Will nip long fins or slow fish when the school is too small, bored, or kept in a short tank.
Predation: Not a predator toward similarly sized community fish; fry and dwarf shrimp are still fair game for most species.
Territory: Holds a patch (cave, corner, or surface). Break sight lines so neighbours can pass.
Planted tanks: good — easy plant ideas
In the glass: typical and warning signs
- A single adult patrols and claims bottom territory in a long tank.
- Resting under cover between patrols is normal ownership.
- Torn fins and chase loops with a second shark mean stocking failed.
- Chronic hiding in a short community cube means footprint failed first.
- Adults punish other rainbow sharks and similar bottom shapes.
- Crowded short tanks redirect territorial strikes onto peaceful neighbours.
- Rehome the second shark the same week damage will not settle.
- Do not add another 'shark' species to keep the first company.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
medium
Diet
omnivore
Rainbow sharks are omnivores that take sinking wafers, quality pellets, and occasional veg or frozen foods at the bottom. Feed after lights soften so the bottom-claiming adult reaches food without a midwater free-for-all. A thin shark in a short tank is usually competition and footprint failure, not a picky strain from the shop.
Shrimp & snails
Shrimp are a gamble with this fish; some ignore them, some clear a colony in days.
Rainbow / red-tailed black shark is fine singly or as a researched pair — check behaviour before doubling up.
- Hold 24 to 28 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 6.5 to 7.5 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 24–28°C without cooking cooler-water tank mates.
- No known fin-nippers paired with long-finned fish unless you accept documented risk.
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 24–28°C reliably.
Plant suggestions
Rainbow / red-tailed black shark does well in planted tanks. Plants compatible with 24–28°C and pH 6.5–7.5:
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. Epalzeorhynchos frenatum
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Epalzeorhynchos frenatum
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Epalzeorhynchos frenatum
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 Rainbow / red-tailed black shark. Each opens a full verdict — not just a list label.
Common questions about Rainbow / red-tailed black shark
- How big do Rainbow / red-tailed black shark get?
- 12 to 15 cm. Stays bottom zone but patrols its territory non-stop.
- What size tank does Rainbow / red-tailed black shark need?
- 150 L minimum. Lateral length matters more than the litre figure; a long footprint cuts aggression sharply.
- Are Rainbow / red-tailed black shark aggressive?
- Rainbow sharks are semi-aggressive and territorial bottom claimants. Calm as juveniles, nastier as mature adults, especially toward other sharks and similar bottom fish. Stress and injury explode when two share a tank or the footprint is too short for patrols.
- What is the most common mistake with Rainbow / red-tailed black shark?
- Buying two rainbow sharks for a large community is how keepers invent a fight until one is torn and injured. One per tank, regardless of litres, is the honest rule for adults. Cute juveniles become territorial fish that punish other sharks and similar bottom shapes without mercy.
- What fish can live with Rainbow / red-tailed black shark?
- This profile currently has no curated unconditional safe-mates shortlist for Rainbow / red-tailed black shark. Other species may still return GOOD in the pair checker, so check the exact pair rather than treating this shortlist as exhaustive. Angelfish, Bala / silver shark, Betta, Boesemani Rainbowfish are conditional (CAUTION): workable only with the specific conditions on each pair page. Run the pair checker for your exact water and tank size before stocking.