While their name can be misleading, rainbow sharks, also nicknamed red-fin sharks, ruby sharks, white-tail shark minnows, and rainbow shark minnows, aren’t actually sharks.
They are tropical freshwater fish native to Indochinese rivers, and are particularly popular in Thailand. They are characterized by their red, vibrant fins, and are known for being territorial.
Rainbow sharks are a great option if you want to add some attitude and color to your aquarium. But you should know that they’re slightly difficult to keep, so they’re most suitable for those who have some experience taking care of fish already.
Rainbow Sharks – Quick Overview
Rainbow sharks originate from the rivers of Southeast Asia, including Malaysia, Laos, Thailand, and Myanmar. These freshwater fish got their name because of their upright triangular dorsal fin on the top, which makes them resemble a shark. Their bright orange/red fins are prominent against their shimmery black/brown/gray body, hence the term rainbow. They generally live for 5-8 years and grow as long as 6 inches once they’re fully mature.
Rainbow sharks prefer plenty of plankton and sandy bottoms. But they also migrate to floodplains during floods or heavy rain.
These fishes are available throughout the year and cost around $3 per fish. And to make sure they thrive well in your aquarium, make sure there are a lot of hiding places, as this helps tone down their territorial behavior.
Rainbow sharks are related to carps and goldfish, but fishing, habitat destruction, and damming of rivers have really reduced their population. You’ll have a lot of fun with rainbow sharks; they can swim slow laps and impose bursts of speed, all within a span of minutes.
Apart from the characteristic “rainbow” colors and an upright dorsal fin with up to 11 branching rays, rainbow sharks have a flat and long stomach with a flat face, a rounded, snout and a forked tail fin. Their eyes are also sunken in on either side of the head. The body is also round near the head and back, but it tapers off towards the tail.
It’s impossible to distinguish male rainbow sharks from female ones until they are sexually mature. Once mature, male rainbow sharks have small black lines on their tail fin and are thinner and more brightly colored than females. Females also have more rounded bellies.
A common color variety of rainbow sharks is albino rainbow sharks that have a white body, with the standard orange/red fins. The albino variant grows almost as long as the traditional rainbow shark, and has nearly the same traits, such as being territorial. The albino rainbow shark might have a yellow or light pink hue in some cases.
Some rainbow sharks also have a dark blue body, but this is not too common.
Rainbow sharks are considered passive in their natural habitat, and they don’t prey on other aquatic animals. However, they’re semi-aggressive in captivity.
Since rainbow sharks are territorial, you can expect behavioral problems like dominance and aggression. This is especially common in mature rainbow sharks. On the contrary, juvenile rainbow sharks are timid and spend most of their time hiding.
Rainbow sharks are also active swimmers and prefer spending most of their time at the bottom of the tank. These bottom-dwellers are also well-known as aquarium cleaners, as they eat the algae growing at the tank’s bottom.
And because they love to stay at the bottom, they tend to fight with other bottom-dwelling fish, including other rainbow sharks, even though they co-exist well with fish that stay towards the top of the tank.
They might headbutt, chase, bite, and tail-butt other bottom-dwellers, but you can reduce these fights by placing your rainbow sharks in a big aquarium with a low fish-to-water ratio.
Also, make sure your aquarium has sufficient hiding places, such as tunnels, rocks, treated driftwood, caves, and hollowed decor. Plants and dense vegetation can also help keep them distracted, which can help reduce conflicts.
Rainbow sharks aren’t known for jumping, but don’t be surprised if they do. Generally, they tend to jump when they’re first placed in the aquarium, so make sure your aquarium has a well-fitted lid so that they don’t jump out.
Since rainbow sharks are active swimmers, we don’t recommend keeping adults in aquariums smaller than 50 gallons. Also, make sure the aquarium has sufficient horizontal space. A short aquarium will only encourage the fish to become more aggressive and territorial.
Generally, if you want to keep multiple rainbow sharks, we recommend opting for a 125-gallon 6-foot-long tank. However, it’s best to only keep one rainbow shark in an aquarium.
These fish thrive well in soft, well-oxygenated water that mimics their natural habitat. They are well-suited to sand, since that’s what’s also present in their native Southeast Asian rivers. But if you prefer using gravel instead, just make sure it’s fine because sharp edges can cut the fish.
You also need to be careful of your tank’s parameters. The pH level should be 6.5 to 7.5, the water temperature should be between 75°F and 81°F, and the hardness should be 5 to 11 DH.
Nitrite and ammonia should also be 0ppm – if it’s even a little higher it will stress the fish and cause diseases. Similarly, nitrate should also not exceed 20ppm. If your water has high levels of chloramine or chlorine, you should treat it with sodium thiosulfate.
In particular, the pH level should be stable, because sudden changes in the pH can make fish more aggressive. So before you introduce them to the new environment in the tank, make sure you allow the water to cycle for two weeks so that it stabilizes.
Place your rainbow shark in the tank as soon as you bring it home; you don’t want it to spend more time than necessary inside the transport bag. Doing so will also help prevent shock and ensure a thriving environment for your fish.
Also, make sure that the tank has moderate water movement, with medium-level lighting. You might also need to install a heater to maintain the water temperature.
Food & Diet
Rainbow sharks are omnivores, so they eat both meat and plants. You should spread their food over two to three sessions a day, and their total feeding time should be roughly 5 minutes.
These sharks aren’t really fussy when it comes to eating, and they eat most things, provided that they sink down to the bottom of the tank.
So, if you plan on keeping rainbow sharks in an aquarium, they will eat live food, vegetables, pellets, frozen food, and flake food without a problem. Meanwhile, they eat insect larvae, algae, and decaying plants in the wild. They also eat small meat chunks present in the river, like zooplankton.
Try to keep their diet varied and give them food from different sources, similar to what they go for in the wild. Give them algae, whether wafers or tablets, live or frozen crustaceans, zooplankton, and insect larvae. For further variation in diet, you can give your rainbow sharks vegetables like peas, zucchini, lettuce, and spinach. This will also help strengthen their immune system.
To maintain their fins’ vibrant orange/red color, regularly give them frozen and live meat, such as brine shrimp or frozen bloodworms.
Variation in diet is especially important if you want your juvenile rainbow sharks to grow up well and have a vibrant color. Lack of variety and an over-restricted diet can lead to poor color expression and stunted growth.
On average, a rainbow shark lives for about 4 to 6 years, but it can also live for as long as 8 years. Your tank’s water quality plays a big role in how long your rainbow shark lives.
A rainbow fish shorter than 4 inches isn’t sexually mature.
In the wild, rainbow sharks mate from October to November, which is also when they reach sexual maturity. But the temperature, length of the day, and changing seasons also affect the exact mating month.
Rainbow sharks reproduce by laying eggs. The female lays eggs, while the male fertilizes them by spraying milt. The eggs then hatch within a week.
Once they hatch, rainbow sharks are merely specks, but they grow very rapidly after that. In just 2-4 weeks, they grow by ½ to one inch. But it can take months for them to mature completely.
However, it is extremely challenging to breed rainbow sharks in an aquarium, and there’s hardly been any success, most likely because of their territorial and aggressive behavior in confinement. Most rainbow sharks available for purchase are bred commercially on farms in Southeast Asia.
Since rainbow sharks are territorial, they tend to stick to the bottom of the tank and chase away other fish that come too close. You need to be careful when choosing tank mates for them.
As mentioned above, you should avoid other bottom-dwellers like catfish, and instead go for fish that stay on the upper or middle levels of the tank. Species larger than or similar to rainbow sharks in size, with a semi-aggressive nature, can tolerate rainbow sharks’ habit of intimidating others.
You should also avoid placing fish that resemble rainbow sharks, like Bala sharks and red tail sharks, in the same tank; otherwise, they’ll terrorize each other.
We also recommend placing the rainbow shark in the tank at the very end so that they don’t try to claim the whole tank and cut down on their hostility.
Here’s a breakdown of compatible and non-compatible tank mates:
Even though both goldfish and rainbow sharks come from the same Cyprinidae family, the two are far from compatible. Both species require a different water temperature, and they have different temperaments. Even if you opt for a goldfish species that prefers warmer temperatures, it will still not co-exist with rainbow sharks because of the latter’s aggressive nature.
Guppies usually only grow up to 2 inches, making them extremely vulnerable to rainbow sharks’ hostile nature. Plus, the latter is most likely to bite the smaller fish. And without a well-fit lid, there’s a high chance of guppies jumping out in an attempt to escape the large fish. So, it’s best not to keep the two together.
You can keep certain cichlids with a similar temperament that are larger or similar in size with rainbow sharks. Semi-aggressive or aggressive cichlids can defend themselves if rainbow sharks disturb them, so both of them can co-exist without problems. The firemouth cichlid in particular is a great choice, and you can even keep a school of them with rainbow sharks.
Angelfish are not great tank mates for rainbow sharks. This is because angelfish have long anal and dorsal fins, as well as 2 elongated ventral fins that a rainbow shark will nip at.
- Betta fish
You should absolutely avoid keeping rainbow sharks and betta fish together. This is because betta fish is very small, making them highly vulnerable to the terrorizing nature of rainbow sharks. Betta fish are also slower than rainbow sharks, so they won’t be able to out-swim the other in a chase, and the shark will try eating the betta’s fins.
- Neon Tetras
These are also small fish and only grow as long as 2.5 inches. And while rainbow sharks are territorial and aggressive, Neon Tetras are the exact opposite. They have extremely peaceful temperaments, which is why they’re highly likely to be terrorized by the larger fish. So if you want to keep the tetras safe, you should keep the two in separate tanks.
Diseases & Treatments
Unsuitable tank conditions can lead to life-threatening health complications in rainbow sharks. Some common illnesses and their causes include:
- Ichthyophthirius multifiliis: A parasitic infection
- Bloat/dropsy: Caused by a bacterial/viral infection, overfeeding, and Hexamita
- Constipation: Due to a lack of fiber in the diet
Since these are common in most aquatic pets, you can treat them on your own.
Rainbow sharks are also vulnerable to the betanodavirus pathogen, which causes viral nervous necrosis. However, to date, there’s no treatment for this disease.
Antibiotics like Prazipro are safe to use for rainbow sharks, but you should avoid medicines containing dyes, salt, and copper. We also recommend isolating sick rainbow sharks in their tank to prevent the spread of infection and to help keep other aquatic animals safe from their increased aggression.
Should you get rainbow sharks?
Rainbow sharks can make for a great addition to your aquarium, but you should take some precautions. Apart from having the right tank conditions, also make sure that you don’t keep them with similar-looking or even the same fish. Despite their territorial and aggressive nature, you won’t have problems with them if you keep them with the right tank mates and the ideal aquarium environment.
And since they are active swimmers and beautiful to look at, it’s quite fun to watch them in the aquarium. Food is not an issue either, as they can eat various food forms.
But if you’re a beginner fishkeeper, we recommend that you look for other options. Some fishkeeping experience is necessary to keep rainbow sharks happy and healthy.
Hi, my name is Adam and I’m an aquarium enthusiast! I didn’t discover the joys of being an ‘aquarium fanatic’ (as some of my friends call me!) until I was in my 20’s. When I first started out I found it difficult to find all the information I needed so I started this website to compile all the useful information I can think of. Enjoy!