rainbow shark care guide header

Rainbow sharks – also known as Red Fin Sharks or Ruby Sharks – are small, tropical freshwater fish that aren’t actually sharks at all. They’re technically part of the minnow family, though you wouldn’t think so when you look at them.

They have vibrant red fins, they’re quite territorial, and though they’re not sharks, their bodies and fins do resemble those of sharks – thus the name. They’re really very interesting little fish that only reach six inches in length.

They’re great for many aquariums, but they do have some specific requirements – especially for Rainbow Shark tankmates – and need potentially moderate care levels, depending on the exact tank setup you choose.

Let’s take a look at Rainbow Shark (like Iridescent Sharks) care, and ask some questions like: Are Rainbow Sharks aggressive? What is the best Rainbow Shark tank size? How big is a Rainbow Shark full grown? What’s the best Rainbow Shark food? How big do Rainbow Sharks get?

Let’s go!

side view of rainbow shark in a fish tank

Quick Intro to Rainbow Sharks

Scientific NameEpalzeorhynchos frenatum
Other Common NamesRuby shark, red-fin shark, red-finned shark, rainbow sharkminnow, green fringelip labeo, whitefin shark and whitetail sharkminnow
Care LevelEasy to Intermediate

Natural Habitat, Identification, and Where to Buy

Natively, Rainbow Sharks come from freshwater river basins in locations in the Indochina region: Mekong, Chao Phraya, Xe Bangai, Maeklong.

These fish are extremely territorial – we’ll talk about this more in-depth later – and very distinct looking. Their long, dark, greenish-gray bodies are shaped like a shark’s body, and their brightly colored fins range in the orange to red realm, giving them the nickname of “rainbow” for the variance in the colors between the different aspects of their colors. Others call them Red Fin Sharks for that marked feature.

The Albino Rainbow Shark may also be of interest to aquarists, as they add another unique layer of coloration and interest to an aquarium. They are less common, of course, but still can sometimes be found on commercial websites and in pet stores. Their bodies range from yellow to white, while their fins go from yellow to red.

Rainbow Sharks are a part of the same family that Goldfish, Carp, and common Loaches belong to.

You can identify Rainbow Sharks by the coloration, but there are a few similar looking fish out there. So, to tell them apart, you can look at the head of the fish.

Rainbow sharks have elongated heads, large eyes with a darkened iris, a well-developed mouth, and something that looks like a mustache over the mouth. This mustache is actually a sensitive sensory antenna that lets them detect food.

Rainbow Sharks have flat abdomens and sharp tail ends that connect with the tail. They also have a slight black streak at the gills, which continues to the mouth.

When you’re ready to buy a Rainbow Shark, you can find them a number of places online, including:

Optimal Water Conditions for Rainbow Sharks

Temperature75 to 81 degrees Fahrenheit
Water Flow RateModerate to fast
pH6.5 to 7.5
Hardness5 to 11 DH

Tank Setup

Minimum Tank Size50 gallons
Optimal Tank Size125 gallons for 2-3
Optimal Tank ShapeLong
Recommended Filter TypeInternal and external

Extra Air Flow and How to Provide It: Adding in additional air stones beyond what you would normally use is the ideal way to get a base level for your air and water flow in the tank. Additionally, you’ll want to add in a wavemaker or powerhead to increase the water flow. But these should be placed for directional flow – like a current – to give a more natural habitat to your Rainbow Shark.

While it’s recommended that you have a minimum of a 50-gallon fish tank for your Red Fin Shark, be aware that they need long aquariums. Most experts recommend an aquarium that is at least 48-inches in length or longer.

If you plan to keep multiple Rainbow Sharks, you’ll need a much longer aquarium, with at least 125-gallons per 2 or 3 fish. It’s not really recommended that you keep multiple Red Fin Sharks together, but we’ll talk about that more below.

You need to make sure that you keep a tight lid on your aquarium with Rainbow Sharks, as they are jumpers.

Creating the Landscape

Rainbow Sharks are territorial fish, so this means you need to keep lots of hiding places for them. Add in some caves, rocks, treated driftwood, hallow decorations, and, of course, plants.

In fact, we highly recommend going with a heavily planted aquarium if you plan to keep Rainbow Sharks. The plants help with a lot of things for these guys, including shelter, distraction from conflict, landscape for healthy bacteria to grow on, and improved filtration.

When it comes to substrate, Rainbow Sharks do best with sand, since this is what’s native to their natural habitat in Asia. Gravel can cause uses for their fins and bodies, since it’s often sharp and jagged. You should specifically avoid anything like crushed coral.

If you do decide to go with gravel for the sake of other fish you keep, make sure that the gravel is very fine, smooth, and polished, instead of “natural” river rock that may harm your Red Fin Sharks.

Best PlantsFreshwater plants that work well with your other aquatic life
Best LightingMedium
Best DecorationsYour best bets with Rainbow Sharks are loads and loads of aquatic plants, treated driftwood, and other caves, hiding holes, and smooth rocks.
Decorations to AvoidAnything sharp, especially on the bottom, will be problematic for your Rainbow Sharks. Make sure everything is smooth and polished. Treat driftwood accordingly.
rainbow shark swimming away in an aquarium

Physiological Considerations

Maximum Size6-inches
Rate of Growth2-3 years for full size, in large enough aquarium
Lifespan5 to 8 years
TemperamentAggressive, territorial
Preferred Tank RegionPrimarily bottom
Scale ThicknessRainbow Sharks have “skin” instead of scales.
Swimbladder ConsiderationsWhile they are hardy fish, they do have a swim bladder like most freshwater fish and tend to be susceptible to swim bladder disorders. It’s important to ovoid overfeeding them. Look for signs of distended belly, erratic swim patterns, or fins close to the body.

Rainbow Sharks are an extremely active species of fish, which is a lot of why they need so much space for moving around in the aquarium. And though they often do hang out at the bottom of the tank, many of them will choose spots in the mid-region of the tank, or even towards the top of the tank. They are jumpers, too, so they may attempt to “break free” from their aquariums.

The Rainbow Shark lifespan is typically between 5 and 8 years, though highly experienced aquarists have claimed to have had Rainbow Sharks for upward of 10 years.


As it has been mentioned, Rainbow Sharks are fairly aggressive fish, so Rainbow Shark compatibility is limited. This is especially true when they are homed with others of their same kind. They are extremely territorial, so other Rainbow Sharks – and other aggressive or semi-aggressive fish – or a similar size or larger will make them feel threatened.

If you provide your Red Fin Sharks with enough hiding spots, enough live plants, and the right aquarium setup in general – along with enough space in a long aquarium – they will be less prone to attacking other fish and get along well with others.

They do generally hang out at the bottom of the tank, and love to nosh on algae along with leftover food from other fish. This makes them a great tank cleaner fish. This also gives an advantage if you want to home these gorgeous fish with others in a community tank – if they live with top and mid-tank dwellers, they’re generally going to do okay with several species.

Do not keep other bottom dwellers with Rainbow Sharks. They will definitely get aggressive with other bottom dwellers.

You also especially do not want to keep more than one male Rainbow Shark in a single tank. They become aggressive towards each other much more often than any other species. Rainbow Sharks are solitary creatures and do not want companions.

It’s also not the best idea for brand new hobbyists to try to keep Rainbow Sharks with other fish, especially other Rainbow Sharks or similar species.

If you do choose to house with other species, make sure the other fish are at least semi-aggressive, as well, or you’ll find your other fish stressed out most of the time. And make sure you have at least five other fish with your Rainbow to avoid one fish getting the brunt of the aggressive behavior.

Some middle and upper tank dwellers that make fair companions for Rainbow Sharks include:

The exceptions to the “no bottom dweller” rule, however are loaches and plecos, because Rainbow Sharks live with these guys in nature. As long as they have enough space, plants, caves, and other tank requirements, they should do fine with these bottom-dweller pals.

Gender, Breeding, and Reproductive Considerations

Rainbow Sharks are far from large fish, but they are certainly some of the larger freshwater aquarium fish that most folks would consider keeping at home. They reach up to 6 inches in normal circumstances, with some reports from advanced fishkeepers having had them grow up to 10 inches.

It’s reasonably easy to tell the male from the female Red Fin Rainbow Shark. Males have thinner, brighter-colored bodies, with easily identifiable black lines on their tail fins. The lines do develop as the fish mature, however, so it’s not as easy to identify the males while they’re still juveniles.

Rainbow Sharks reach sexual maturity after one to two years of life, but they often continue growing until they are three or four years of age.

If you’re hoping to breed more, you’re almost completely out of luck. The species is next to impossible to breed without very specific, expensive requirements, and beginning hobbyists most certainly won’t be able to manage the process. The aggressiveness of the species makes breeding excessively difficult, so fish farms actually have to use pheromones and injections in many cases.

When mating does occur, the female lays her eggs and allows her chosen mate to fertilize them with a milt spray. The Rainbow Shark eggs then are left to develop for a week before they hatch.

Nutritional Needs

Rainbow Sharks are like most other bottom dwellers. They’re omnivores who tend to scavenge for leftover food, algae, and similar food sources. Specifically, they go after periphyton, crustaceans, phytoplankton, zooplankton, and algae when possible, as well as insect larvae, and other natural sources of protein.

It’s tempting with this sort of fish to just let them eat whatever finds its way into their mouths. However, it’s important to make an actual effort to ensure the fish are receiving the full nutrition they need.

This means several things:

  1. Be sure that all of the fish in your aquarium are being fed high-quality, grain-free (or as close as you can find) fish pellets and flakes or gel food.
  2. Supplement their diets with high-quality protein foods, algae wafers, et cetera, to ensure a well-balanced diet.
  3. Mix things up with a variety of Rainbow Sharks food choices, instead of just feeding one type of food to your fish all the time.

To ensure your Rainbow Shark diet is spot on, it’s also important to make sure that you use sinking pellets or flakes, or the top and mid-dwelling fish will be the only ones who get the high-quality food before it starts to spoil.

And if you have juvenile Rainbow Sharks, meat is especially important to their physical development, so make sure you’re giving a high-protein diet for their dining. Without it, their growth will be stunted, their vibrant colors won’t be so vibrant, and overall, your Rainbow Sharks will be in poor health.

Since they’re scavengers (like starfish), they eat more than what you feed them, so overfeeding them is pretty easy to do. Be sure to keep a close eye on the food you give them and remove anything that isn’t eaten within two minutes of feeding time.

So, if you’re asking “what do Rainbow Shark eat?” I’ve got a quick breakdown for you.

Best Sustenance Food TypeHigh-quality pellet or flake, low to zero grains included
Additional Food for Optimal HealthFrozen or freeze-dried bloodworms and brine shrimp, fresh vegetables – such as spinach and lettuce, or boiled peas or zucchini – insect larvae, crustaceans, algae wafers, tubiflex worms, periphyton, zooplankton, daphnia, artemias, small insects
Special Foods and Considerations for Best Color and GrowthA full spectrum of the protein foods for juveniles is particularly necessary for vibrant health and coloring.
When and How Often to Feed Fish Based on Life CycleThere are mixed answers on this because each shark is a little different. Start with once per day and see how your fish does with this. If the aggression is voracious towards food, increase feedings to twice per day, keeping an eye out for any additional changes.

Common Diseases and How to Avoid and Treat Them

Thankfully, Rainbow Sharks a pretty hardy little species of fish. They are not, of course, immune to diseases, however, so it is important to keep an eye out for symptoms of diseases. And since these are freshwater Rainbow Shark, they are most likely to suffer from common freshwater fish ailments like Ich, swim bladder disorder – or SBD – and fungus and skin flukes.

The most common issue with Rainbow Sharks is poor water quality. They have specific parameters that need to be met with their water quality, so be sure to keep an eye on these with your testing kits, thermometer, et cetera.

Avoiding the illnesses altogether are your best treatment for these fish. Make the regular maintenance and water changes a priority. Being a bottom dweller doesn’t alter their need for pure, fresh water.

It’s also important to avoid over feeding your fish and to only use high-quality foods. Both can cause multiple health issues, as well as change the water quality in your fish tank.

Best Antibiotics: Those safe for minnows and others in the Cyprinidae family – freshwater fish. Prazipro is safe and works well.

Treatments to Avoid: Anything containing copper, salt, dyes. Avoid use of Paraguard – which contains Malachite Green, which Rainbow Sharks do not respond well to.

Food Recommendations When Sick: Maintain a healthy balance with strong emphasis on protein and fresh vegetables.

Hospital Tank or Isolation Within the Community Tank Specifics: Remove from community tank. Since they are aggressive fish, they are prone to being extra aggressive when ill and may attack other fish to preserve self.

3 More Things to Know About Rainbow Sharks

  1. Some fish keepers have reported Rainbow Shark full sizes up to 10-inches.
  2. Albino Rainbow Shark size is the same as standard Rainbow Sharks – typically between 5 and 6-inches, if housed in a large enough tank for full growth potential.
  3. The Rainbow Shark was originally described by H.W. Folwer in 1943 and was classed in the Labeo genus as a frenatus. It wasn’t until 1998 that it was reclassed in its current genus of Epalzeorhynchos.

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