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), Rainbow shark, Ruby shark, Red-tailed black shark (fish. Not a true shark)
Fishori provides conservative planning guidance, not guarantees.
Based on multiple reputable aquarium care sources with strong agreement. Use the numbers here as planning defaults — your room, water, and routine still shape real-world outcomes.
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.
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.
Top things that go wrong
- Fin-nipping risk in typical community layouts. Fin-nipping risk toward long-finned or slow tank mates when the school is understocked, bored, or kept in a tank too short to spread out in.
- Shrimp & snails. Shrimp: depends on the individual fish. Some leave them alone, others hunt cherry shrimp down within a week of meeting them.
Common mistakeBuying two for a large community. Two rainbow sharks fight until one is injured. One per tank regardless of volume.
What most shops don't tell you
- 1.Spawning, breeding, or rearranging territory can make normally calm fish surprisingly aggressive in short tanks or with rival shapes.
- 2.Large minimum volumes still need real footprint: length and width for turning matter as much as the litre number on a sticker.
- 3.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.
- 4.Multiple 'sharks' in 120 L, leading to chronic chasing and tattered fins.
- 5.Housed with red-tailed black shark lookalikes in the same territory band without the footprint to separate them.
- 6.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.
- Giant danio200L min · same group, comparable tank size
- Rosy Barb180L min · same group, comparable tank size
- Denison's / red-line torpedo barb250L min · same group, similar adult size
- Denisons Barb250L min · same group, similar adult size
- Scissortail Rasbora150L min · same group, similar adult size
- Gold / Chinese barb120L min · same fish family
- Odessa Barb120L min · same fish family
- Banded leporinus300L min · same fish family
- Angelfishalso intermediate semi-aggressive, similar tank size
- 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 on file yet.
Plan grid
Key limits are shown above; this section adds planning detail: pH band, swim level, bioload and activity, and the radar.
Swim zones
Planning trait chart
Six indices for comparing species on paper before you spend.
- Beginner ease32
- Peacefulness22
- Community fit6
- Small-tank fit90
- Hardiness54
- Energy86
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Common setup sketches
Conservative patterns from Fishori fields — still run the pair checker for every species you add; sketches are not a stocking guarantee.
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.
Tank mate intelligence
Pair with mid- and top-zone fish (rainbowfish, danios, larger tetras, gouramis). Avoid red-tailed sharks, other rainbow sharks, slow long-finned fish.
Pair-level compatibility with this fish as anchor.
Read the blocking rule on each pair page before experimenting.
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Rainbow / red-tailed black shark + Boesemani Rainbowfish
Behaviour, temperament, and what to watch
Prose and lists come from the same record: read temperament first, then glass-level signals so you are not surprised after day three.
Semi-aggressive and territorial. Calm as a juvenile, nasty as a mature adult, especially toward similar-shaped fish.
Stress / aggression triggers on file
- Small groups or boredom
- Long-finned or slow tank mates
- Bare tanks without structure
Fin nipping: Fin-nipping risk toward long-finned or slow tank mates when the school is understocked, bored, or kept in a tank too short to spread out in.
Predation: Not a predator toward similarly-sized community fish. The usual community caveats about mouth size still apply for very small fry or shrimp.
Territory: Holds territory on substrate, in caves, or at the surface film. Break the line of sight with hardscape, and avoid placing the tank where the fish can see its own reflection.
Planted tanks: good — easy plant ideas
In the glass: typical and warning signs
- Busy at feeding time — expects food to hit the water predictably.
- Clamped fins, gasping at the surface, hiding non-stop, or refusing food after the first week.
- Rapid breathing when parameters swing — fix ammonia/nitrite first, then reassess mates.
- Chasing one individual repeatedly, torn fins on tank mates, or food theft every feed.
- Corner guarding, flaring, or body-blocking — territory is normal until it becomes relentless.
- Separate or rehome if injuries appear, one fish is pinned, or feeding becomes a daily chase.
- If water is stable but behaviour worsens, reduce stocking or remove the highest-impact species first.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Care parameters: water, food, inverts, grouping
Chemistry and group rules sit here so you are not re-reading the same line from tank mate or temperament blocks. Swim level is in the plan grid above.
Hardness
medium
Diet
omnivore
Mixed diet: a quality flake or pellet as the staple, with frozen or live foods two or three times a week.
Shrimp & snails
Shrimp: depends on the individual fish. Some leave them alone, others hunt cherry shrimp down within a week of meeting them.
Kept singly or as a paired setup. Check the species profile before doubling up in one tank.
Breeding behaviour depends on the species. Research before you buy a mixed-sex group of this fish.
- 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
Same library as the rest of Fishori: tank-mate index for this species, category peers, guides, and litre-based stocking lists where min tank on file is within the hub volume.
Plan with tools
Pair-level rules and multi-fish stocking use the same conservative engine — add this fish in the tank builder only after mates pass pair checks.
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:
Profile status: partially verified · Evidence tier: high · 3 linked source(s). Fishori does not fabricate citations.
Fishori uses conservative planning rules based on these sources.
Confidence is explained in the summary at the top of this page (same tier as here), not repeated below.
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.
- Fishori profiles work from typical aquarium trade sizes and hobby care norms. Specialist site checks and literature review for this species are not yet recorded here, so the ranges on this page are planning numbers rather than guarantees.