The Rainbow Shark (Epalzeorhynchos frenatum), also called the Ruby Shark or Red Finned Shark, is a freshwater fish native to Thailand. It is most commonly found in the Mekong, Maeklong, Xe Bangai and Chao Phraya basins. The waters are fast flowing and the climate is tropical. Rainbow Sharks are not actually sharks; they are named so due to their shark-like body shape and dorsal fin.
Rainbow Sharks are a popular freshwater tropical fish among experienced fish keepers. They are not expensive to purchase, however, their aggressive nature towards other Rainbow Sharks means not all pet stores and aquatic centers are able to stock them. They range in price from $3 to $10.
Rainbow Shark Lifespan
A healthy Rainbow Shark can live in excess of 10 years, but since most individuals are sold as juveniles, you can expect your Rainbow Shark to live between 5 and 8 years if they are kept in optimum tank conditions.
Adult Rainbow Sharks will reach 5-6” but are sold as juveniles around 2”. Beginner fish keepers do not always realize how big their Rainbow Shark will grow. They are easily recognized by their blueish-grey or black bodies and orange-red fins and tail. The Red-tailed Black Shark is almost identical except only its tail is red. Its other fins are the same dark color as its body.
It is not possible to identify gender until Rainbow Sharks reach sexual maturity. Males are brighter than females and develop dark lines on their tail fin. Females tend to have thicker bodies.
Thanks to selective breeding, there is an albino strain of this species. These Rainbow Sharks still have the orange-red fins and tail, but their body is pale pink or white and their eyes are red. They exhibit the same aggressive behavior and grow to the same size as normal Rainbow Sharks. They are also popular are can be purchase from pet stores, aquarists or breeders but may be more expensive.
A Rainbow Shark is so called because it has a long body tapered towards the tail, a pointed snout and flattened abdomen, just like marine sharks. Rainbow Sharks also have downturned mouths, as they are bottom feeders, sifting through the riverbed in search of food.
Rainbow Shark Tank
Tank size is crucial to the health and welfare of Rainbow Sharks. They are territorial, so they need a long rectangular tank that will provide the space they need to establish a territory. Your tank must be at least 50 gallons for one Rainbow Shark and 4 feet long. If you plan on keeping a community tank with multiple species of fish, 55 gallons would be better. Although not recommended, a tank with multiple Rainbow Sharks should be a minimum of 125 gallons and 6ft long. Ideally, there should be space for a neutral section within the tank.
Since Rainbow Sharks are bottom feeders, they need a fine substrate material. The rivers they are native to have fine sand beds so this is the perfect tank substrate. Sand has the added advantage of being easy to clean as food and fish waste cannot collect within it.
You can also use fine gravel as an alternative, but it is not as fine as sand, so waste will collect. If you choose to use gravel you will need to clean it regularly to maintain good water hygiene. Never use large gravel as the edges can be sharp and will injury the fish’ mouth if they get picked up during feeding.
Plants and Decorations
Driftwood is a great decoration for a tank containing Rainbow Sharks. They have lots of gaps and holes that create hiding spots. Providing places to hide reduces the chances of confrontational behavior within the tank community. You can also include hollow cave decorations or tunnels as additional hiding spots. Adding areas of dense vegetation is also a good idea and gives a more natural look to your setup.
Rainbow Sharks are from a tropical climate so the water temperature needs to be kept between 73-80°F. The sweet spot is 77°F but anywhere with this range is fine as long as the temperature is kept stable. Fluctuations can lead to stress. You will also need to consider the temperature needs of other fish if you have a community tank of multiple species. Invest in a good quality heater that will maintain the desired temperature.
There are no specialist lighting requirements for Rainbow Sharks. A simple aquatic LED light will do the job just fine. Be sure to keep your lighting on a natural day/night cycle either with a timer or by manual switching off the lighting during the night.
The pH level needs to be between 6.5 and 7.5 for Rainbow Sharks to be happy. Never put tap water straight into the tank. You need to put it through a dechlorinator first. You can purchase chlorine test from any aquarium, pet store or online. Regular water changes will remove waste from the tank. A build up of waste can increase the nitrate levels of the tank, which is harmful for fish.
Rainbow Shark Health
Rainbow Sharks are sturdy little fish and only at risk of common problems such as Swim Bladder issues as well as Fungal infections. Keeping your tank parameters stable, within the right ranges and completing regular water changes will prevent most diseases from occurring. Fungal and bacterial illnesses are almost always due to chemical imbalances.
Healthy Rainbow Sharks are bright colored and have glossy/bright eyes. They will spend time sifting the substrate along the tank floor looking for food and when feeding time comes, they will have a good appetite.
Rainbow Shark Food & Diet
These fish are omnivores, so require both fish flakes or pellets and live food. You need to use fish food that will sink to the bottom. A few times a week you should also feed crustaceans, aquatic or insects. Good options are bloodworms, mosquito larvae, brine shrimp and daphnias. You could also consider keeping a live food colony. Blackworms are easy to maintain and would provide a source of enrichment for your Rainbow Sharks and other omnivorous fish you may keep in the same tank.
Finely chopped spinach, cucumber and raw peas are also good options to feed a few times weekly. As long as they are feed one food source daily, they will be happy. Never feed more food than your Rainbow Shark can eat in one sitting.
Behavior & Temperament
Rainbow Sharks are territorial and will set up their own territory within the tank. They will spend some time each day on the tank floor sifting through the substrate. They are a tank-cleaner species and will also graze on algae if you let a small amount grow in the tank.
They need places to hide to rest and get away from other fish within the tank. Juveniles are generally quite placid, but aggression will begin to show as they reach maturity.
Rainbow Shark Aquarium Mates
In the wild they do not show aggression towards other fish, but in tank conditions Rainbow Sharks are aggressive towards their own kind, fish that look similar to them and also smaller fish.
If you are wanting to keep multiple species choose fish that are the same size or slightly bigger than an adult Rainbow Shark. Fish that dwell in the upper or middle levels of the aquarium are safe choices:
- Clown or Zebra Loaches (no other bottom dwellers)
- Neon or boeseman’s rainbowfish
Keeping more than one Rainbow Shark in the same tank is not recommended, however, if you do choose to, you must not have a tank smaller than 6ft in length. 125 gallons are larger would be the minimum so they have plenty of space for their own territories with a space between that is neutral.
Rainbow Shark FAQ
- Will rainbow sharks kill other fish?
They are a semi-aggressive species and are capable of killing smaller fish.
- Are Rainbow Sharks aggressive?
Yes, with other Rainbow Sharks or fish smaller than themselves.
- What can live with a rainbow shark?
Other semi-aggressive species the same size or larger.
- Are rainbow sharks bottom feeders?
Yes, they swim slowly along the bottom sifting through the substrate in search of food.
- Do Rainbow Sharks bite?
They will bite the fins of other smaller fish.
- Do Rainbow Sharks need a heater?
They do, the optimum tank temperature is 77°F.
Rainbow Sharks are a great and colorful addition to a tropical freshwater tank, provided you have researched suitable tankmates and your tank parameters are in the required ranges.
They do not need as much careful maintenance as other species, just regular water changes and a small daily feed to keep them happy and healthy.
The most important thing is to provide a long enough tank. The majority of Rainbow Shark keepers go wrong because their tank is too small to allow for territories to be formed. This can lead to confrontation, fights and injuries.
A good sized tank, stable tank parameters and a healthy varied diet will make for a calm and relaxed tank environment that your Rainbow Shark will enjoy.