Looking for an active, colorful species to add to your aquarium? The popular freshwater rainbow shark (Epalzeorhynchos frenatum) might not be as imposing as an actual shark, but it sure will add life to your aquarium.
Rainbow sharks are often the victim of improper housing and care, kept in small aquariums and with improper tankmates. So what do they actually need to thrive?
This care guide contains everything you need to know in order to keep your rainbow shark healthy.
About Rainbow Sharks
Here are a few things that you’ll need to know if you’re considering keeping keeping a Rainbow Shark:
Appearance & Size
Despite its common name, the rainbow shark is obviously not actually a type of shark. Rather, it’s a member of the small genus Epalzeorhynchos, which also contains the popular red-tailed black shark (Epalzeorhynchos bicolor).
The genus is commonly referred to as ‘sharks’ due to its members’ body shapes: their elongated body, flat belly area and pointed dorsal fin does make them slightly resemble actual marine sharks. The rainbow shark can reach an adult size of around 6”.
The rainbow shark is characterized by its differing colors. Although they will always possess red-orange fins, their body color can vary from black to blueish or grey.
Some sources report body color is likely partly dependent on the health of the fish, with paler coloration being a sign that it’s stressed or sick. As we’ll discuss below, there are also a few selectively bred color variations out there.
The genus Epalzeorhynchos contains four species, three of which can be found in the aquarium hobby.
Luckily, it’s not too difficult to distinguish between these species and successfully identify the rainbow shark. The flying fox (Epalzeorhynchos kalopterus) features brown coloration without the typical red finnage.
The rainbow shark and red-tailed black shark look more similar to each other, but can be told apart from their fins. Rainbow sharks will have orange-reddish color on all of their fins, whereas this coloration is limited to the tail on the red-tailed black shark.
Note that generally, the red-tailed black shark is more commonly found in aquarium stores than its rainbow shark cousin.
It’s worth searching for a rainbow shark though, as their temperament is generally a little more mellow than that of their red-tailed cousins.
Selectively Bred Colors
Selective breeding has resulted in an albino rainbow shark form, which is now commonly sold.
Additionally, the patented GloFish brand has recently started producing four varieties of glowing rainbow sharks (blue, green, orange and purple).
These sharks’ bright colors are produced by genetic modification and their care is identical to that of regular rainbow sharks.
Rainbow Shark Temperament
As mentioned earlier, the rainbow shark is a better choice than the relatively aggressive red-tailed black shark when it comes to temperament. However, it still doesn’t make the ideal community fish.
Although they might seem quite timid while still small, rainbow sharks are known for becoming more territorial and aggressive when they grow.
Their main problem is with similar-looking species: other rainbow sharks and anything that looks too much like them won’t be tolerated.
The shark’s behavior towards other tankmates is generally more laid-back, although it might still pick on and chase after fish that inhabit the same water layer.
To find out how to stock a community aquarium that contains a rainbow shark while avoiding open war, skip to the section on tankmates.
Rainbow sharks are naturally found in Southeast Asia and appear most common in Thailand.
The species inhabits the Mekong, Chao Praya and Mae Klong river basins, where it sticks to areas with sandy substrates that make suitable grazing spots for bottom feeders.
Rainbow sharks are known to be migratory and will move up into flooded areas during the wet season. Once the dry season rolls back around, they will then migrate back to their normal river habitat and spend the rest of the year there.
Rainbow Shark Lifespan
Although the rainbow shark can likely reach quite a respectable age (in excess of 10 years), the sad reality is that most specimens don’t live to see more than a fraction of that.
As mentioned in the intro this species is almost always sold at its small juvenile size without inclusion of proper information about the care it requires.
Small aquariums, improper stocking and the stress resulting from these are likely the primary premature rainbow shark killers. If you want your shark to live to its full potential, it’s important to provide more than just the bare minimum!
Rainbow Shark Care
Rainbow sharks aren’t the hardest fish to keep, but they do require some specific care. Here are some things you should know about rainbow shark care:
With a maximum size of around 6 inches, rainbow sharks are not among the largest aquarium fish out there. This doesn’t mean they’re suitable for keeping in small aquariums, though.
Their activity level is quite high and they will spend much of their day browsing all around the aquarium for food.
Sources vary greatly when it comes to aquarium size for rainbow sharks, with some suggesting that an aquarium size of as little as 20 gallons will be enough.
Unfortunately, this is not the case and the stress of being kept in such tight quarters will likely affect your rainbow shark’s health and lifespan. Instead, go for something quite a bit larger.
Aquarium length is more important here than volume, since a bottom feeding species like this won’t make much use of vertical space.
An aquarium length of around 47” is to be recommended, which for a rectangular aquarium comes down to a minimum volume of around 60 gallons.
Like many other aquarium fish species the rainbow shark will appreciate the presence of plenty of cover in its aquarium.
You can opt to set up a biotope-style tank that resembles a river by using a sandy substrate covered in boulders and pebbles of various sizes, as well as possibly a few live plants. Top it off with at least two natural looking cave structures, as the rainbow shark appreciates having a quiet and dark place to sleep.
If you’re not concerned with replicating the natural habitat of your rainbow shark, the fish will still thrive just fine as long as you provide hiding places. Plenty of live plants work well to enhance its feeling of security, and you can offer caves and tubes for sleep-time refuge.
A rainbow shark that feels safe will be a happy rainbow shark, and a happy rainbow shark will be a mellow one.
Serious aggression problems can arise if your rainbow shark is uncomfortable in its environment, so again: cover is the key to success here.
It is sometimes noted that rainbow sharks can have an appetite for live plants, but it seems that in reality this won’t be too much of an issue in most cases.
In any case, make sure your rainbow shark is well-fed and stick to hard-leaved plants like Anubias or Java fern if you’re concerned.
Although it’s not necessarily a must to install extra powerheads in your aquarium, it’s important to keep in mind that rainbow sharks hail from flowing waters that contain high amounts of dissolved oxygen. In the aquarium, it’s important to imitate this in order to help your rainbow shark feel comfortable.
Promoting oxygen exchange can usually easily be done by pointing the filter outlet to the water surface or installing an extra air stone.
Those that are serious about the biotope aspect might opt for a small powerhead to achieve the ‘flowing river feel’.
If your rainbow shark spends more time at the surface than usual, it might be time to invest in a more powerful filter as oxygen is likely lacking.
In the wild, rainbow sharks inhabit fast-flowing and clean waters. In the aquarium this means they’re not very tolerant to bad water quality.
You’ll have to make it a point to keep up with maintenance, doing weekly water changes and testing the water on a regular basis.
As always the tank should be fully cycled before introducing any fish species, and this especially applies to the sensitive rainbow shark.
When it comes to acidity and hardness the rainbow shark is less fussy. It can take a relatively wide range here, although sticking around neutral is probably your best option.
The desired water temperature falls in the normal tropical range.
Rainbow Shark Diet
As their body shape and downturned mouth suggest, rainbow sharks are bottom feeders. In the wild, they’ll scour the river floor for any edible morsels they can find.
They’ll do the same in the aquarium, but because our tanks are simply too clean to sustain a rainbow shark you’ll have to supplement its diet with daily feedings.
Because rainbow sharks are omnivores it’s important to offer plenty of variation. A sinking pellet food will work well as a staple, but don’t forget to also switch things up regularly.
You can opt for frozen foods like mosquito larvae or bloodworms or even consider setting up a live food colony. Blackworms, for example, are quite easy to maintain and your rainbow shark will love the variety.
In addition to pellets and meaty foods, try offering blanched vegetables like zucchini and spinach.
Some aquarists also like to use extra strong lights on their aquarium to promote algae growth for their rainbow shark to browse on, or grow algae separately by submerging rocks and placing them under powerful lights for a couple of weeks.
Rainbow Shark Tankmates
As discussed earlier, contrary to its red tailed black shark cousin the rainbow shark can be a relatively good neighbor.
That being said, it won’t do well in just any type of community and you’ll have to strongly keep this species in mind while selecting other fish.
Don’t be fooled by the withdrawn appearance of juvenile rainbow sharks in the aquarium store: the fish will become increasingly assertive with age. When combined with incorrect tankmates it can cause enough mayhem to prove fatal to the more fragile species.
The most important thing to keep in mind when you’re choosing tankmates for your rainbow shark is that they should not resemble rainbow sharks in any way. It’s suspected that this species is solitary in the wild, only meeting members of its own species when it’s time to mate.
Each rainbow shark appears to maintain a territory of its own, which it will strongly defend from anything that looks too much like another rainbow shark.
Some aquarists report that merely seeing the color red sends their shark into a frenzy! As such, it’s recommended to keep no more than one rainbow shark in your aquarium in some cases.
Exceptions would be very large tanks, but even then we still personally wouldn’t attempt to keep multiple rainbow sharks together.
In addition to not looking like a rainbow shark, any tankmates should be able to stand their ground. These sharks are active and feisty, plowing through groups of other fish without paying any mind to them and sometimes appearing to chase tankmates just because they can.
Other bottom feeding species are best off avoided in most cases, as they’ll be too close to the rainbow shark’s territory and will be stressed out by the constant harassment.
If you do want to keep your rainbow shark with other bottom dwellers then consider loaches, which appear to get along relatively well with this species.
Other than that, it’s recommended to stick with sturdy schooling fish that inhabit the middle and upper water layers.
A few examples of species that have successfully been kept with rainbow sharks are:
- Loaches: zebra loach (Botia striata), yo-yo loach (Botia almorhae), clown loach (Chromobotia macracanthus)
- Barbs: rosy barb (Pethia conchonius), cherry barb (Puntius titteya)
- Danios: zebra Danio (Danio rerio), giant Danio (Devario aequipinnatus)
- Rainbowfish: Boeseman’s rainbowfish (Melanotaenia boesemani), neon rainbowfish (Melanotaenia praecox)
Breeding Rainbow Sharks
Unfortunately, we can be rather short about rainbow shark breeding. Although some aquarists have reported seeing their rainbow sharks spawn in the aquarium, we haven’t found any reports of this actually resulting in fry.
The aquarium environment is likely simply too different from the species’ natural habitat.
Additionally, in most cases it’s preferable to keep rainbow sharks solitarily anyway, because as we’ve discussed they aren’t very keen on being accompanied by their own species.
Pretty much all rainbow sharks in the aquarium trade are most likely commercially bred, but unfortunately this requires the use of hormone treatments.
Everything taken together, rainbow sharks can be a wonderful addition to your aquarium.
They are more peaceful than the more commonly seen red tailed black shark, making them a better option for communities.
That being said, this species does require more care than most sources like to make their readers believe. Your rainbow shark will need a large aquarium, pristine water quality and suitable décor in order to thrive.
If you do provide what it needs, it will be a lively addition for your aquarium for years to come.