Rainbow Shark: Care Guide, Feeding, Size and Tankmates

Rainbow Sharks, also known as Red Fin Sharks or Ruby Sharks, are small tropical freshwater fish native to Thailand.

They are known for their vibrant red fins and being territorial.

If you’re looking to add some color and attitude to your aquarium this may just be the fish for you.

In this article we will discuss how to care for them, dietary needs, tank mates/compatibility, breeding and much more.

Let’s start with a quick summary before we move on to discuss their appearance and compatibility with other fish.

Category Rating
Care Level: Easy/Moderate
Temperament: Semi-aggressive
Color Form: Gray, Red
Lifespan: 5-8 Years
Size: Up to 6″
Diet: Omnivore
Family: Cyprinidae
Minimum Tank Size: 50 Gallons
Tank Set-Up: Tropical Freshwater: Rocks, Caves or Plants
Compatibility: Moderate. Get along with many other freshwater fish species

Overview of Rainbow Shark

The Rainbow Shark is a tropical freshwater cyprinid that is somewhat difficult to keep. It would be suitable for fish keepers who have a few years of experience and are looking to expand their aquarium.

They are known for their territorial nature and bright vibrant red fins.

Originating from the warm rivers of Southeast Asia, they were given the affectionate common name of Rainbow Shark, due to their upright dorsal fin which gives them the appearance of a shark.

You should expect your Rainbow Shark to grow up to 6 inches in length and have a lifespan of 5-8 years.

In terms of cost you should be looking to spend no more than $3 per fish, and they are readily available all year round.

If you do intend to keep Rainbow Sharks you should make sure your aquarium has plenty of hiding places for them as this helps to reduce their territorial behavior.

Rainbow Shark

Rainbow Sharks’ Appearance

The Rainbow Shark is a dark gray fish with vibrant red/orange fins.

They have a long, flat stomach with a pointed snout and an upright dorsal fin. It’s this fin which gives them the appearance of a shark.

The Rainbow Shark is a small fish which you should expect to grow up to around 6 inches when fully matured.

It is not possible to identify their gender whilst they are juveniles. You have to wait until they are sexually matured.

Once sexually matured females will have thicker bodies, and males will develop small black lines on the tail fin. Whilst males will be thinner, they will generally have brighter colorations.

A common variety of the Rainbow Shark is the Albino Rainbow Shark.

Whilst the Albino Rainbow Shark maintains the red/orange fins, its body is white. It will grow to a similar size as a traditional Rainbow Shark and matches several of their characteristics including being territorial.

Typical Behavior

The Rainbow Shark is a territorial fish which can cause certain behavioral problems such as aggression and dominance.

This generally happens as they mature. As juveniles they are timid and will spend large periods of their time hiding.

They are active swimmers and tend to spend most of their time dwelling at the bottom of the tank. Due to them being bottom-dwellers, they are known as aquarium cleaners as they will eat the algae growing on the bottom of the tank.

You should make sure your aquarium is long and has plenty of space for your Rainbow Shark to swim on the same level.

Whilst they are peaceful with fish that dwell in higher water, they are known for fighting with bottom dwelling fish, including their own kind.

Such behavior can include biting, chasing and head-and-tail butting.

You can attempt to reduce this behavior by ensuring they are placed in a large aquarium, with a low fish to water ratio. You should also ensure they have lots of hiding places, such as caves, tunnels and other hollowed décor.

Finally, whilst they aren’t renowned for jumping, it isn’t unheard of. For this reason you should make sure your lid is well fitted to prevent them jumping out of your aquarium. Jumping generally occurs when they are first placed in the aquarium.

Habitat and Tank Requirements

As mentioned in the overview section, Rainbow Sharks are tropical freshwater fish that originate from Thailand.

They are active swimmers so adults should not be kept in aquariums smaller than 50 gallons. The aquarium should also have plenty of horizontal space. If the aquarium is too short in length it will encourage them to become more territorial and aggressive.

If you plan on keeping multiple Rainbow Sharks then you should use at least a six foot long, 125 gallon tank (however we don’t recommend keeping more than one Rainbow Shark per aquarium; more on this later).

Due to the Rainbow Shark’s territorial nature, you should ensure your aquarium has lots of hiding places for them. Think caves, treated driftwood and rocks.

Dense vegetation and plants also work. Plants can be used to keep them distracted so it will reduce conflict and also help prevent algae.

As for substrate, they are best suited to sand, as this is what is found in their native Thai rivers. Be careful if you intend to use gravel because the sharp edges can cut them. If you do decide to use gravel make sure it’s very fine.

Finally, you should make sure your aquarium lid is fitted well, they are can jump!

Tank Conditions

You should keep it within the follow parameters: 75°F to 81°F, pH level 6.5-7.5 and a water hardness of 5 to 11 DH.

With Rainbow Sharks you need to keep the pH level stable. Sudden changes in the pH level can cause them to become more aggressive than usual.

Lighting should be kept at a medium level, and the water movement should be moderate.

Rainbow Shark in Aquarium

Compatibility and Tankmates

Let me preface this section by stating if you are looking for a calm community fish, the Rainbow Shark might not be the fish for you.

Whilst they will get along with many other freshwater fish species, they are very territorial and this can be overwhelming for more shy species, such as Marbled hatchet fish and Otocinclus catfish.

As mentioned in the aquarium and habitat section above, they like to take possession of an area of the aquarium; generally the small caves and rocks.

We sympathize with any fish that stumbles upon a Rainbow Shark’s territory! They will be extremely aggressive and chase the intruders away.

Due to their aggression, you need to be careful when choosing tank mates.

As a general rule they aren’t aggressive towards species that don’t look like Rainbow Sharks. As the Rainbow Shark dwells at the bottom of the aquarium, avoid other bottom-dwelling fish such as cichlids and catfish. You should also avoid any similar looking fish, i.e. Red Tail Sharks and Bala Sharks.

When selecting tank mates, look for those fish that dwell in the middle and upper levels of the aquarium.

You also want to pick fish that can defend themselves and have a calm but strong personality. Species such as Gouramis, Barbs, Danios and Rainbowfish are all compatible with Rainbow Sharks.

Finally, a little compatibility trick you can use is: make sure the Rainbow Shark is the last fish placed in your aquarium. This will prevent it trying to claim the entire aquarium as its own and should reduce territory problems.

Keeping Rainbow Sharks with other Rainbow Shark

As a general rule it’s recommended that you only keep one Rainbow Shark in an aquarium at any time. Red Tail Sharks should also be added to this rule.

Like the Royal Gramma, Rainbow Sharks will not tolerate living with its own kind.

In the wild they generally lead a solitary lifestyle and are very territorial. In a normal aquarium there just isn’t enough space and the larger Rainbow Shark will chase the smaller Rainbow Sharks relentlessly until it kills them.

This territorial nature develops with age, so if you get two juvenile Rainbow Sharks they could very well start out getting along, but their relationship will decline rapidly as they mature.

If you insist on keeping more than one Rainbow Shark follow these guidelines:

  • You should keep a group of them (5 or more). This way the dominant Rainbow Shark has multiple fish to chase.
  • Never keep just two Rainbow Sharks.
  • If you intend to introduce more than one Rainbow Shark make sure each has at least a meter of separated territory.

Diet and Feeding Requirements

As mentioned during the overview, Rainbow Sharks are Omnivores which means they eat both plants and meat.

In the wild they generally consume decaying plants, algae, insect larvae and small chunks of meat they find in the river such as Zooplankton.

They aren’t fussy eaters and will consume most things; providing it sinks to the bottom of the tank!

This is good news if you plan to keep Rainbow Sharks in aquariums. They will eat flake food, frozen food, pellets, vegetables and live food with no complaints.

You should aim to keep their diet varied and feed them a variety of food sources, similar to what they would eat in the wild. For instance: algae (tablets or wafers), insect larvae, crustaceans (frozen or live) and zooplankton. To keep their diet varied you can also offer them plenty of vegetables such as spinach, lettuce, zucchini and peas; this will keep their immune system strong.

If you want to make sure their red/orange color is a vibrant shade, regular meals of live and frozen meat should be given to them; frozen bloodworms and brine shrimp will be fine.

This is even more important for juvenile Rainbow Sharks. If you want your juveniles to grow large with vibrant colors, make sure their diet is varied and never overly restricted. Lack of variation can cause stunted growth and poor color expression.

As for their feeding regime, you should aim to spread their food out over 2-3 sessions a day. The total length of feeding time should be around 5 minutes.

If food is left after this time, you are feeding them too much and it will impact your nitrogen cycle.

Rainbow Shark Breeding

In the wild, Rainbow Shark’s tend to mate during October to November, which is when they also reach their sexual maturity. However the exact month can be impacted by changing seasons, and depends on the length of the day and temperature.

Note: You can assume that if the fish is less than 4 inches in length, they aren’t sexually mature yet.

Rainbow Sharks reproduce through egg laying. The female will lay eggs and the male will then fertilize them by spraying the eggs with his milt. From here the eggs will hatch within the week.

Unfortunately though, breeding Rainbow Sharks in an aquarium is extremely challenging and we are yet to hear of any success stories.

Again, this is more than likely because of their aggressive and territorial nature in confined settings.

The majority of Rainbow Sharks you find available for purchase will be bred in commercial farms based in Southeast Asia.

Is the Rainbow Shark Right For Your Aquarium? (Summary)

The Rainbow Shark would make a great addition to your community providing they aren’t kept with the same, or similar looking fish.

Whilst they are known for being territorial, providing you give them a suitable aquarium environment and match them with the appropriate tank mate(s), you shouldn’t have too many problems with them.

They are a beautiful fish and an active swimmer, so will provide you with enjoyment when watching them in an aquarium.

They are good eaters and will eat a variety of food forms including pellets, flakes and frozen meat.

If you are planning to keep Rainbow Sharks, you should also make sure that you’ve got some fishkeeping experience already, as these fish generally aren’t for beginners.

Do you keep Rainbow Sharks? Let us know in the comments section below…

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