Caring For Rainbow Sharks: Tankmates, Feeding, & Diseases

Rainbow sharks are the fish equivalent of clickbait. When you see them in stores they’re colorful, small, cute, and active…. and most beginners can’t resist them. So you grab a 10-gallon tank and load up on neon-colored gravel, guppies, and cory cats.

But rainbow sharks get big. And when they get big, they get mean. Don’t get me wrong, they can be mean at a smaller size too, but less weight to throw around generally means they’ll stick to bullying smaller, easily intimidated fish like guppies and corys.

So, obviously they make terrible community fish, right?

But as long as we’re defining a community as “several different species living together” and not as “whatever you feel like dumping in the tank”, they’re not the worst community fish, either. However, rainbow sharks – like all “sharks” – are territorially aggressive. Particularly aggressive towards other sharks or anything that has a similar look.

At this point, it’s important to note that rainbow sharks – occasionally called ruby sharks or redfin sharks – (Epalzeorhynchos frenatum) are not the same as red-tail sharks (Epalzeorhynchos bicolor), or redfin sharks (Epalzeorhynchos munense) – which are also sometimes called ruby sharks. Which just adds to the confusion, of course.

However, in most cases when someone says “ruby shark” or “redfin shark” they’re referring to rainbow sharks. In any case, we have binomial nomenclature to keep things straight.

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Table of contents

Distribution & Natural Habitat

They’re native to Thailand, Laos, Cambodia, and Vietnam. In Thailand, it’s found in Mae Klong, Chao Phraya, and Mekong river basins. Laos populations are found in the Mekong drainage – above and below the Khone Phapheng Falls – including the lower Xe Bangfai. Reports of them being found in Cambodia in the lower Mekong may actually be misattributed to E. frenatum, and are thought to actually be E. munense.

In either case, most of these reports are thought to be outdated or attributed to the wrong species, so their true extent in the wild is unknown – but both CARES and IUCN indicate this fish isn’t under any immediate threat in the wild.

Most of the time, rainbow sharks have been observed grazing sandy or rocky substrates in streams and rivers. However, they do move into seasonal floodplains.

Aquarium Care

Rainbow sharks straddle the line between an easy fish and an intermediate fish. At smaller sizes, they’re much easier and more manageable, but once they become larger and more aggressive, you need a bit more experience to determine what’s acceptable aggressive behavior and when you need to intervene.

They also need substantial oxygen and water movement and they don’t handle poor water quality, and the larger they get, the more water quality becomes an issue.

Tank Specs

A 60-gallon is the minimum for one rainbow shark. They’re large, active fish that are capable of swimming surprisingly fast, they’re also highly territorial and get large, so a 90-gallon would be your best bet if you want to keep your rainbow shark with other large tank mates.

They’re also capable jumpers, so you’ll want to make sure their lid is secured. Especially when they get larger because they’re heavy enough to remove the lid without any issues.

Depending on how hot you keep your house, you may be able to get away without a heater, but I would suggest one set to a low temperature even if you keep your house pretty warm just to be safe.

Because you need a large tank, you’re going to want to opt for an in-line heater instead of a submersible heater for efficiency. Most in-line heaters have controller issues, so I highly recommend an external controller with your in-line, but that’s your call.

If you’d like more detailed information or more heaters to look at, you can check my detailed review of the best aquarium heaters, but I included the best picks for you below.

Stocking

You’ll likely only want one rainbow shark for your tank. If you have an excessively large tank, you might be able to keep large numbers of rainbow sharks together. Some people report it going successfully, but if that’s the route you want to take you’ll need a 200-gallon (or larger) and eight or more rainbow sharks to spread out the aggression.

And don’t expect it to be a nice, peaceful tank. It’s going to be a battleground.

I don’t suggest this method – at all – but if that’s the route you’re determined to take, that’s how you’d need to do it.

Decor

Rainbow sharks do best in densely planted tanks, it helps break up sightlines, define territories, and lessen aggressive behaviors. This is particularly true with much smaller rainbow sharks, but even adult rainbow sharks could benefit from substantial plant coverage if you can.

Driftwood, rock structures, and other places to hide are also helpful for reducing aggressive behaviors.

They’re not picky about substrate, sand, pebbles, gravel, bare bottom, or planted substrates all work fine. Though sand and gravel are the most natural if you’re going for a biotope setup and you’ll see much more natural grazing and browsing behaviors with those two substrates. HTH pool filter sand is my favorite, but I’d buy it in-store if you can so you don’t have to pay for the shipping.

If you’re planning on getting high-maintenance plants, the best planted substrates are included below for you.

Best Plants For Rainbow Sharks

Though it’s not particularly hard to find plants that work well in your rainbow shark tank, you’ll want to avoid low-light and floating plants. Mostly for water movement and algae issues, it’d just be easier, but they still wouldn’t be a terrible choice. Additionally, if you want to see their natural behavior, you’ll want to avoid carpeting plants so your shark can pick through the sand and rocks for algae and aufwuchs.

Some plants that would help promote their natural behaviors are;

Java Moss

Guppy Grass

Lemon Bacopa (Bacopa Carolinia)

Broad Leaf Amazon Sword (Echinodorus bleheri)

Vallisneria

Lighting & Filtration

Lighting isn’t super important for rainbow sharks, but stronger lighting would help algae and aufwuch development, which would give them an opportunity to graze in your tank like they would in the wild. But if your shark seems intimidated by the brighter lighting, you can dampen it a bit with a dimmer or swapping it out for a cheaper light. I have the best adjustable lights listed below for you.

As for filtration, rainbow sharks are intolerant of low oxygen levels and any pollutants like ammonia, nitrite, or nitrate, so you’ll likely want a canister filter. You can opt for a HOB, but I don’t suggest it. Most HOBs will struggle to turn over the water at 6x – 8x per hour.

Depending on your tank size, you’ll be looking at a filter in the range of 360GPH or above. If this is too much for your smaller shark, grab an adjustable canister filter and you can slowly up the volume as it grows.

Water Care

Like any fish that comes from fast-flowing water, rainbow sharks don’t tolerate waste in their water very well. Depending on your tank size, filtration, stocking levels, and the size of your shark, you’ll likely need to do at least 20% weekly water changes. Though 30% would be better if you can.

Because we’re talking about a 60+ gallon tank, you’ll likely want to grab a python to change their water because the bucket method would be unreasonable at those volumes for most people.

You’ll also need your usual dechlorinator, salt, and a few meds on hand in case they get sick. Because these guys don’t have any illnesses that really stand out, I don’t suggest stocking up on anything super-specific. General Cure, Erythromycin, and Ich-X should be a good start to cover most of your bases.

Feeding Rainbow Sharks

Rainbow sharks aren’t fussy with food. They will appreciate the presence of algae and aufwuchs in the tank – particularly when they’re younger – but as they get older they tend to slow down on their browsing habits. Still, you’ll want to include some greens in their diet.

Repashy soilent green is a good option, but so are omnivore pellets, bloodworms, mysis shrimp, krill, and anything else that will sink to the bottom for them. You’ll want to avoid flakes with these guys – like with most fish – because most of them are terrible and they’re not nutrient-dense enough for it to be worth your money.

They’ll also eat some common veggies like lettuce, cucumbers, zucchini, green beans, and anything you’d likely feed your pleco. Be sure to quickly blanch your veggies first (boil them in hot water for 1 – 3 minutes then dump them in ice water or run them under cold tap water) before you add them.

Again, they’re not picky, but you’ll want to include as many food options as you can afford to give them a nice balanced diet. Three is a great starting point, but more is always better when it comes to an animal’s diet!

Rainbow Shark Diseases

Rainbow sharks are pretty resilient and there aren’t a ton of diseases that seem to pop up again and again for them. Of course, like any fish, they can get any freshwater disease, but the most common diseases I’ve seen them get are listed below for you:

Bloat

Ich (White Spot Disease)

Swim Bladder Disease (SBD)

Constipation

10 Of The Best Rainbow Shark Tank Mates

You’ll want to add you rainbow shark last. This will prevent them from claiming the entire tank and relentlessly harassing any intruders you decide to add later. You’ll also want to avoid fish that are small, shy, bottom-dwelling, or easily intimidated. Remember these guys get pretty big, so you’ll want to plan your tank with the shark’s end-size in mind, which typically means other large fish or small typically obnoxious fish.

It’s also worth noting that female sharks tend to be much more tolerant of interlopers than males, so you’ll probably have more success with a female than you would a male. And, finally, because sharks need a lot of water movement, you’ll need fish that can handle the current.

So without any further preamble, here are the best rainbow shark tankmates:

Bristlenose Plecos (Ancistrus sp.)

Breeding Rainbow Sharks

Rainbow sharks haven’t been bred in captivity without the use of hormones and, even then, they’ve only been bred commercially. We don’t know much about their breeding habits, but we do know they’re egg layers that exhibit no paternal care and they reach sexual maturity around 4″.

Males will typically have redder fins than females, but males also exhibit grey lines on their caudal fin. Females don’t have any lines on their caudal fin and they tend to be “chunkier” looking than their male counterparts. But these distinct characteristics don’t usually become apparent until the fish are sexually mature.

In subadults, you can typically see whether they’re male or female by the shape of their anal and dorsal fins. Females tend to have more rounded fins while males have more angular or pointed dorsal and anal fins.

Types Of Red-Fin Sharks

There are a few colors of rainbow sharks available right now, though most of them aren’t natural mutations. It’s also important to note that redtail and ruby sharks (noted at the beginning of the article) are different species, not color mutations.

Further Reading & Resources

VIN – A Multi-Pronged Approach to Streptococcosis in Rainbow Sharks (Epalzeorhynchos frenatum) and Redtail Black Sharks (E. bicolor)