Quick answer: Buy a red-tailed black shark or rainbow shark only if the tank holds at least 120 litres. A silver shark, also sold as a bala, needs 300 litres and 180 cm of length. Skip iridescent sharks and other fish that outgrow home glass.
Rainbow and red-tailed black sharks need at least 120 litres; silver sharks need 300 litres and 180 cm. This page is a desk comparison of published care numbers and current tank specs. We did not house these fish, open tanks in a lab, or treat sick animals.
The Litre-and-Length Cutoff
We include a species only when OATA publishes a home-tank volume and the adult length is 35 cm or less.
That cutoff rests on two public records that anyone can check. OATA’s freshwater-shark sheet sets the tank volumes, and FishBase lists a 35.0 cm standard length for the silver shark, Balantiocheilos melanopterus.
We left out any fish OATA says grows too large for most aquariums. We also left out marine sharks, pond carp sold as sharks, and starter kits that fail the published length.
A product is in only if the maker lists a numeric capacity on a current page. That capacity must serve a tank of 120 litres or more. Nano boxes and flake-only foods did not make the table.
Our research team compared those published numbers and converted litres to U.S. gallons and centimeters to inches. We did not invent sizes, dosages, or flow readings.
The three species OATA treats as home aquarium sharks
OATA names three common freshwater “sharks,” and none of them is a true shark.
They are carp relatives in the family Cyprinidae from south and southeast Asia. Most fish in shops are captive bred, according to that same OATA sheet.
The three species are:
- Red-tailed black shark, Epalzeorhynchos bicolor
- Rainbow shark, Epalzeorhynchos frenatum
- Silver shark, Balantiocheilos melanopterus, also sold as a bala shark
OATA says red-tailed black sharks and rainbow sharks grow to around 15 cm, which is about 5.9 inches. Keep those two singly, because they get territorial as they age.
OATA says the silver shark grows upwards of 30 cm, and FishBase lists a maximum of 35.0 cm standard length, about 13.8 inches. Silver sharks are shoaling fish, and OATA says keep them in groups of at least five.
FishBase records the IUCN Red List status for this silver shark as Vulnerable. The assessment date on that FishBase page is 7 February 2019.
OATA lists two other trade names that fail our cutoff. The black shark and the iridescent shark both grow too large for most aquariums, so they are out.
True marine sharks are out, and so are roseline barbs sold as “sharks.” OATA does not publish a home volume for those fish on this sheet.
Tank size is a length problem, not a gallon slogan
Gallon labels mislead buyers because these fish need a long swimming lane more than a round gallon number.
OATA’s volume floors are:
- At least 120 litres for one red-tailed black shark or one rainbow shark
- At least 300 litres and 180 cm of length for silver sharks
Our research team converted those figures for U.S. tanks:
- 120 litres is 31.7 U.S. gallons
- 300 litres is 79.3 U.S. gallons
- 180 cm is 70.9 inches
FishBase adds a second length check for the silver shark. Its aquarium-keeping note calls for a tank longer than 150 cm, which is 59.1 inches, and a group of five or more.
A 32-gallon box can meet the 120-litre volume and still be too short, so length is the number to check first.
The Fluval Flex 32.5 Aquarium Kit lists 32.5 U.S. gallons, or 123 litres, which is 3 litres above OATA’s 120-litre floor. The same page lists a length of 32.5 inches, or about 83 cm. That clears the volume rule and fails every silver-shark length rule we used.
The Fluval Roma 240 Bluetooth LED Aquarium Kit lists 63 U.S. gallons, or 240 litres. The maker’s Roma page lists the tank at 47 inches long, which is 120 cm. Volume clears OATA’s 120-litre floor, but length is 60 cm short of OATA’s 180 cm silver-shark rule.
So the Roma 240 can be a volume match for one rainbow shark or one red-tailed black shark. It is not a silver-shark tank under OATA’s length rule.
If you want a silver shark group, plan for a large rectangle at least 180 cm long. A 79-gallon slogan is not enough if the glass is only as long as the Roma 240’s listed 47 inches.
Filters, food, and kits we compared
We compared five current products whose maker pages list numeric specs that can serve a 120-litre or larger tank.
| Product | Maker-listed size | Key listed spec | Role under our cutoff |
|---|---|---|---|
| Fluval Flex 32.5 Aquarium Kit | 32.5 U.S. gal / 123 L | 32.5 in long | Volume clears 120 L; length is short for silver sharks |
| Fluval Roma 240 Bluetooth LED Aquarium Kit | 63 U.S. gal / 240 L | 47 in / 120 cm long | Volume clears 120 L; 60 cm short of OATA’s 180 cm rule |
| Fluval 307 Canister Filter | 40–70 U.S. gal | 303 U.S. GPH pump output | Fits a 120-litre class tank |
| Fluval 407 Canister Filter | 50–100 U.S. gal | 383 U.S. GPH pump output | Fits a 300-litre class tank |
| Hikari Tropical Algae Wafers | 17.0–18.0 mm sinking wafer | 33.0% min. crude protein | Sinking algae diet OATA describes |
Fluval’s 07 Series page lists the 307 for 40 to 70 U.S. gallons. Pump output at 120 V / 60 Hz is 303 U.S. GPH, or 1,150 LPH. Filter circulation on that page is 206 U.S. GPH, or 780 LPH.
The same page lists the 407 for 50 to 100 U.S. gallons, with pump output of 383 U.S. GPH, or 1,450 LPH. Filter circulation is 245 U.S. GPH, or 930 LPH.
Our research team divided that 245 U.S. GPH circulation by OATA’s 300-litre silver-shark minimum, which is 79.3 U.S. gallons. The result is about 3.1 tank volumes per hour on paper, which is a spec comparison and not a live flow reading.
Hang-on-back filters can work on a 120-litre tank if the maker rates them for that volume. Our hang-on-back filter setup guide walks through cartridge changes on that style of filter.
OATA says red-tailed black sharks and rainbow sharks appreciate sinking pellets with high algae content. Hikari’s Algae Wafers page lists a 17.0 to 18.0 mm sinking wafer. Guaranteed analysis on that page starts at 33.0% minimum crude protein and 4.0% minimum crude fat.
Feed what they can eat in a few minutes, once a day, per OATA. Silver sharks take flakes and granules when small, then larger pellets as they grow.
The Flex kit also lists a 214 U.S. GPH pump output and 63 LEDs, which can grow tough plants if you keep the midwater open. See our beginner planted-tank plant list for species that tolerate current.
Water, plants, and a weekly routine
OATA’s parameter band is the water target for this group, and those numbers beat a guess from a shop sticker.
Copy these numbers from that sheet:
- Temperature: 22–27°C, about 72–81°F
- pH: 6.5–8.0
- Ammonia: 0 mg per litre
- Nitrite: 0 mg per litre
- Nitrate: not more than 20 mg per litre above your tap water
- General hardness: 4–12°dH
- Carbonate hardness: 3–10°dKH
If your tap sits below 6.5, raise pH in small steps. Our guide to raising aquarium pH covers buffers and change size. Do not chase a single decimal if the fish already sit inside 6.5 to 8.0.
OATA wants a heater year-round and a tank kept off drafts, heat vents, and direct sun. Use a tight lid, because silver sharks jump.
Use sand or fine gravel, since OATA flags barbels as easy to scrape on coarse rock. Add caves or pots for the two territorial species, and leave a long open lane for the silver shark group.
Live plants are ideal for cover, and plastic plants are an allowed stand-in on that sheet. Do not pack the tank so tight that a 30 cm fish cannot turn.
OATA’s weekly routine is short:
- Test ammonia, nitrite, nitrate, pH, and hardness.
- Change 25% of the water.
- Treat new tap water with a conditioner before it goes in.
- Rinse filter media in the old tank water, not in raw tap water.
That 25% change is a published dose, not a guess. Skip mouth-siphoning, because OATA says to use a primed gravel cleaner.
Species and tanks we refused to cover
We refused every fish that fails the 35 cm length cap or lacks an OATA home volume on this sheet.
That list includes:
- Iridescent sharks and black sharks, which OATA says grow too large for most aquariums
- Marine sharks of any size
- Chinese high-fin banded sharks kept as pond fish
- Roseline “sharks” with no volume on this OATA sheet
- Two rainbow sharks or two red-tails in one small tank
OATA says those two territorial species are best kept singly. Mixing both in one 120-litre tank also fails the rule, because each fish needs its own 120 litres under a strict reading.
We also refused nano kits under 120 litres. The Flex 32.5 is in the table only as a volume check, and it is not a silver-shark recommendation.
We did not rank products or sort them by price. The table is an attribute match against OATA’s litres and centimeters.
Sexing these fish at home is not reliable, and OATA says it is very difficult. We did not add breeding steps, because that sheet says home tanks rarely give enough space.
Never dump leftover fish or plants into local water. OATA states that release is illegal in its jurisdiction and can harm wild habitats, and the same caution applies in the United States.
FAQ
These questions are the ones shop labels leave unanswered after you read OATA’s litres and FishBase’s 35.0 cm length.
Are aquarium sharks real sharks?
No, OATA states they are not related to marine sharks. They are cyprinids, which are carp and minnow relatives from south and southeast Asia. The “shark” label is a shop name for the body shape.
What tank size does a rainbow shark need?
OATA recommends at least 120 litres for a rainbow shark, which our research team converted to 31.7 U.S. gallons. Check length as well. A 123-litre Flex kit meets volume and is only 32.5 inches long, a short lane for an active 15 cm fish.
Can I keep two rainbow sharks together?
OATA says rainbow sharks and red-tailed black sharks are very territorial and are best kept singly, not in pairs or groups. A second fish of the same type needs its own 120 litres and its own caves.
How big does a bala shark get?
OATA says the silver shark, the bala, grows upwards of 30 cm. FishBase lists 35.0 cm standard length, about 13.8 inches, so plan the tank for that adult rather than the juvenile in the bag.
How many bala sharks should I buy?
OATA says silver sharks should be kept in groups of at least five, and FishBase repeats a group of five or more. One lonely silver shark in a short tank fails both sources.
What should I feed freshwater sharks?
OATA calls them omnivores and says red-tailed and rainbow sharks should get sinking, algae-rich pellets. Hikari Tropical Algae Wafers list 33.0% minimum crude protein and a 17.0 to 18.0 mm wafer. Feed once a day what they finish in a few minutes.
Can I keep an iridescent shark in a home tank?
OATA says the iridescent shark grows too large for most aquariums. It fails our 35 cm cutoff, so do not buy it as a “starter shark.”
