rainbow sharks

Caring For Rainbow Sharks: Tankmates, Feeding, & Diseases

Reading Time: 8 minutes

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.

Epalzeorhynchos frenatum
Epalzeorhynchos frenatum (redfin, ruby, or rainbow shark)
Epalzeorhynchos bicolor
Epalzeorhynchos bicolor (redtail shark)
Epalzeorhynchos munense
Epalzeorhynchos munense (redfin or ruby shark – if any common name is listed at all)

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

rainbow shark care

FAQ

Rainbow Shark Classification

IUCN Status:  Least Concern – last assessed 3/28/11

Class: Actinopterygii are ray-finned fishes, which is a subcategory of boney fishes. These fish are characterized by the bony structures that support their webbed fins. This group makes up nearly half of all living vertebrates.

Order: Cypriniformes includes over 400 genera (the plural for genus) and more than 4,200 species of carp, minnow, loaches, and relatives.

Family: Cyprinidae, or collectively called cyprinids or the “carp family,” is composed of egg scattering species that exhibit no parental care.

Genus: Epalzeorhynchos includes only four species; rainbow shark (Epalzeorhynchos frenatum), redtail shark (Epalzeorhynchos bicolor), redfin shark (Epalzeorhynchos munense), and flying fox (Epalzeorhynchos kalopterus.)

Species: Epalzeorhynchos frenatum 

What does Epalzeorhynchos frenatum mean?

The jury’s still out, but Epalzeo- could mean curative, which seems unlikely, or horn, which would refer to their cone-shaped protuberance on their nose. While -rhynchos would mean snout or beak.

Frenatum, on the other hand, likely comes from frenatus, meaning bridled. Likely in reference to the black “bridle” lines from their horn snout beak up to their eyes.

Putting it together gives you “bridled horn snout.” Which is… just odd.

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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.

Thailand, Kanchanaburi, Mae Khlong basin
Thailand, Kanchanaburi, Mae Khlong basin

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

Difficulty: Intermediate
Size: 6″ (15 cm)
Lifespan:  5 – 8 years
Tank Size: 60 gallons (240 liters)
Diet: Omnivore
Temperature: 68 – 80 F (20 – 26 C)

pH6.0 – 7.5
Hardness:  2 – 15 dKH
Temperament: Territorial/Aggressive
Breeding: Not been done in private aquarium
Swimming: Everywhere
Availability: Common

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.

insta in-line ehater
Ista In-Line Heater

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.

this is sparta gif

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 Fern

Java Fern

Java fern is a nearly indestructible low light plant that can put up with tons of abuse. It doesn’t need Co2, fertilizers, or fancy soils. There are tons of lush, beautiful, jungle-like aquascapes you can create with it too!

Difficulty: Bulletproof
Growth: Slow
Temperature:  64 – 86F (18 – 30C)

pH: 5.0 – 8.0
Hardness:  2 – 25 dKH
Placement: Anywhere, basically

Java Moss

Java moss

Java moss is an almost bulletproof plant that requires almost no care. It doesn’t grow nearly as slowly as it’s java fern cousin, and can create lush moss beds that blow and billow in the current. They’re a great option for grazers, fry, or those of you with the blackest of thumbs.

Difficulty: Easy
Growth: Moderate
Temperature: 59 – 86F (15 – 30C)

pH: 5.0 – 8.0
Hardness: 3 – 12 dKH
Placement: Floating or attached

Hornwort

Hornwort care

Hornwort is a bushy, versatile plant that’s great for keeping the after clean. It thrives in nearly every environment, so long as it doesn’t freeze, it’ll survive and grow. It does best if left floating, but can be planted.

Difficulty: Bulletproof
Growth: Fast
Temperature: 63 – 86F (18 – 30C)

pH: 5.0 – 8.0
Hardness: 2 – 25 dKH
Placement: Floating or weighted

Lemon Bacopa (Bacopa Carolinia)

Bacopa carolinia

It’s as bulletproof as Java fern, but grows as fast as hornwortBacopa carolinia is truly the best of both worlds if you’re looking for a hardy species you can plant in the substrate. It grows up to 40″ (not a typo) and propagates quickly, which is great for larger tanks that need a ton of cover on the cheap.

Difficulty: Bulletproof
Growth: Fast
Temperature:  64 – 86F (18 – 30C)

pH: 5.0 – 8.0
Hardness:  2 – 25 dKH
Placement: Background

Broad Leaf Amazon Sword (Echinodorus bleheri)

echinodorus bleheri

Echinodorus bleheri is one of a few species that get the catch-all common name of “Amazon sword.” Like most swords, you’ll need to keep the crown exposed when planting it. It also needs high light and a decent amount of nutrients to grow well.

Difficulty: Easy
Growth: Moderate
Temperature:  71 – 82F (22 – 28 C)

pH: 6.5 – 7.5
Hardness:  2 – 25 dKH
Placement: Planted, background

Vallisneria

Vallisneria

Vals come in a ton of varieties, but most of them are about the same to grow. They can grow rapidly, and quickly cover your tank with lush, kelp-like forests for your fish. Some species, however, do grow much shorter than others.

Difficulty: Easy
Growth: Moderate
Temperature: 63 – 82 F (17 – 28 C)

pH: 6.5 – 8.5
Hardness: 3 – 30 dKH
Placement: Planted

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.

python
Python

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.

rainbow shark eating cucumber

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

fish bloat

Bloat certainly doesn’t have to be as severe as the picture, but you get the idea. Bloating is an accumulation of gas, fluids, or unpassed food present in the fish. Although I have no proof, I suspect this is why most people search “how to tell if [insert fish species] is pregnant” even if they can’t get pregnant. There is a difference between a bloated fish and a fish that’s eaten too much – the fish that ate too much will act normal whereas the other usually won’t.

Symptoms:

  • Your fish’s stomach is distended without raised scales
  • Fish may appear to be in some sort of discomfort and avoid swimming or other usual activities
  • May not be pooping

Causes:

  • Intestinal blockage
  • Constipation
  • Internal bacterial infection
  • Internal growths/tumors

Ich (White Spot Disease)

ich fish disease

Ich is caused by a parasite that, to many, looks like tiny white pimples across the fish. It can attach to the mouth, fins, body, and gills. You can usually see fish scraping themselves against objects (likely because parasites are itchy!) before white spots even appear.

Symptoms:

  • White spots
  • Scratching
  • Redness or bloody streaks

Causes:

  • Ichthyophthirius multifilis (parasite)

Swim Bladder Disease (SBD)

Swim Bladder Disease (SBD)

If your fish is swimming oddly, is having trouble swimming, or seems to be unable to control the direction it’s going in – it likely has a swimbladder issue. 

There are numerous reasons why fish develop this (and not all of them are understood) so treating SBD can be hit-or-miss depending on why it got it in the first place.

Symptoms:

  • Floating upside down
  • Sinking to the bottom of the tank
  • Standing on their head
  • Inability to keep upright

Causes:

  • Bacterial infection
  • Cysts
  • Fatty liver tissue
  • Egg bound (females)
  • Parasites
  • Diet-related issues

Constipation

Constipation fish

Constipation usually clears up on its own, but some remedies include feeding blanched or canned peas to herbivores. For omnivores or carnivores, brine shrimp and daphnia (live, if you can) are usually a quick and painless fix for both of you. Salt baths may also be suggested in severe cases.

Symptoms:

  • Stringy, white, and/or clear feces
  • Bloating
  • Lethargy

Causes:

  • Hexamita (HITH)
  • Lack of fiber

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:

Congo Tetra (Phenacogrammus interruptus)

congo tetra

Wild populations are endemic to the Congo River in Africa, but thankfully, we have plenty of captive-bred fish on the market. They do best in groups of at least six.

pH: 6.0 – 7.5
dKH: 3 – 18
Temp: 73 – 82 F (23 – 28 C)

Size: 3.2″ (8 cm) max
Temperament: Peaceful shoaler
Swimming: Mid to top

Dwarf Neon Rainbowfish (Melanotaenia praecox)

Dwarf rainbowfish do best when kept in groups of at least 6, though more is always better. Once they’re fully mature and settled, they develop beautiful colors when given lots of plants and open space to swim.

pH: 6.8 – 7.5
dKH: 5 – 15
Temp:  73 – 82 F (23 – 28 C )

Size: 3.2″ (8 cm)
Temperament: Peaceful and active
Swimming: Top to midwater shoaling

Malabar Danio (Devario aequipinnatus)

One of a handful of species you can find sold under the name “giant danio,” this species’ care is very similar to all the other large danios. They typically come from streams in the wild and need a decent amount of dissolved oxygen and water movement. They’ll also need to be kept in shoals of six or more in a large tank so they have space to swim.

pH: 6.0 – 8.0
dKH: 2 – 15
Temp: 65 – 80 F (18 – 26 C)

Size: 3.2″ (8 cm)
Temperament: Peaceful, active, shoalers
Swimming: Mid to top

Tiger Barb (Puntigrus tetrazona)

Tiger barbs are active, hardy fish that aren’t easily intimidated or pushed around. They do have a reputation for being nippy – and obnoxious – and they need to be kept in groups of eight or more to really reduce those behaviors, but six as a minimum is recommended.

pH: 6.0 – 7.0
dKH: 5 – 12
Temp: 75 – 82 F (24 – 28 C)

Size: 3″ (7 cm)
Temperament: Active shoalers
Swimming: Mid to top

Diamond Tetra (Moenkhausia pittieri)

Diamond tetras make a great addition to most community tanks, but they can be nippy. They’re typically peaceful, active, unfussy, and generally mind their own business. They do best in shoals fo 6 – 8. If there’s more than that, they tend to nip tankmates instead of eachother.

pH: 5.5 – 7.0
dKH: 5 – 12
Temp: 75 – 82 F (24 – 28 C)

Size: 2.4″ (6 cm)
Temperament: Peaceful shoalers
Swimming: Mid to top

Buenos Aires Tetra (Hyphessobrycon anisitsi)

buenos aires tetra

Buenos Aires tetras have a reputation for being a bit nippy when kept in smaller numbers. Stocking them somewhere in the 8 or more region usually solves this issue. They’re active, outgoing, and hardy tetras that can handle a wide range of water conditions.

pH: 5.5 – 8.5
dKH: 1 – 20
Temp: 61 – 83 F (16 – 27 C)

Size: 2 – 2.5″ (5 – 6 cm)
Temperament: Active and outgoing
Swimming: Top to midwater shoaling

Bristlenose Plecos (Ancistrus sp.)

bristlenose pleco

Most plecos aren’t suited for the average aquarium, some growing up to two feet long – not the bristlenose pleco. They’ll happily munch on algae, green beans, zucchinis, cucumbers, sinking algae wafers, and of course leftovers and fish poo – although leftovers and poo make for a literally shitty diet.

pH: 6.0 – 7.5
dKH: 6 – 10
Temp: 60 – 80 F (15 – 27 C)

Size: 4 – 5″ (10 – 12 cm)
Temperament: Peaceful, can be territorial
Swimming: Everywhere that has structure

Severum (Heros efasciatus)

green severum
Green severum

Severums do best when kept in groups of 5 – 6 other severums and, with the exception of breeding, they’re peaceful fish. When maintained alone, they can become nasty towards tank mates. They do, however, need a large tank to be housed in groups.

pH: 6.8 – 7.5
dKH: 5 – 15
Temp:  73 – 82 F (23 – 28 C )

Size: 12″ (30 cm)
Temperament: Peaceful
Swimming: Everywhere, but usually mid to bottom

Orange Head Geophagus (Geophagus sp. ‘orange head’)

A currently undescribed, but already well-loved species of Geophagus, these guys do best in groups of 5 – 6 and are super peaceful as far as geos go. They only get aggressive when spawning and, like all geos, they require sand.

pH: 4.5 – 7.5
dKH: 1 – 10
Temp:  79 – 86 F (26 – 30 C )

Size: 9.8″ (25 cm)
Temperament: Peaceful
Swimming: Mid to bottom

Bichirs (Polypterus sp.)

senegal bichir

Bichirs, affectionately called “pollys,” are thought to be living fossils and some reports indicate they might be a missing link between water-dwelling species and species who eventually migrated onto land – though there’s little evidence to support it. 

Senegal bichirs (pictured), ornate bichirs, and marbled bichirs are some of the most popular options.

pH: 6.2 – 7.8 – species dependent
dKH: 5 – 20 – species dependent
Temp: 75 – 82 F (24 – 28 C) – species dependent

Size: 12 – 39″ (30 – 97 cm)
Temperament: Somewhat aggressive towards other fish, aggressive towards own kind
Swimming: Bottom

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.

fullgrown female rainbow shark
Female rainbow shark, note the bulkier body, orangish color on the fin, and lack of grey lines on the caudal

subadult male rainbow shark
Likely a younger male, not quite at full maturity, but note the slimmer build, brighter red, and the grey lines on the caudal

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.

female rainbow shark
See more rounded anal and dorsal fins
male rainbow shark
More pointed anal and dorsal 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.

rainbow shark colors

Normal

Normal-colored rainbow sharks’ fins are all red (all 7 of them) and their body ranges from a deep bluish black when they’re young to a grayish purple color when they’re fully grown.

albino rainbow shark

Albino

Albino rainbow sharks are all white, expect for their fins – which are an orange to reddish color. Some have colorless fins, though this is pretty rare.

glofish rainbow sharks

GloFish

GloFish rainbow sharks come in four colors, currently. They act just like normal rainbow sharks but they’ve been spliced with marine creature DNA some time back (typically jellyfish, but occasionally some other DNA.)

Further Reading & Resources

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

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