The Complete Rainbow Shark Care Guide (Epalzeorhynchos frenatum)

The rainbow shark (Epalzeorhynchos frenatum) is a small freshwater fish native to Southeast Asia. But despite its name, it’s not actually a shark and belongs to the Actinopterygii family (ray-finned fishes). While these fish are popular in the aquarium hobby, they are not suited for a beginner and should only be kept by an experienced fishkeeper.

While these fish are often advertised as ‘algae eaters’, the amount of algae they consume is far less than plecos or other commonly available algae eaters (Read The 3 Best Algae Eaters for Your Aquarium here). Most fishkeepers who purchase these fish as algae eaters are often disappointed.

Care Level:	Difficult
Temperament:	Semi-aggressive
Life Span:	6 Years
Size:	6 inches (15 centimeters)
Minimum Tank Size:	30 gallons (110 liters)
Temperature:	75-80°F (24-27°C)

Habitat

Rainbow sharks are native to Asia and are found in Cambodia, Laos, and Thailand, with some sources claiming a small population exists in Vietnam. These fish were first described in 1937 (Fowler, Labeo erythrurus).

Rainbow sharks are bottom and midwater dwellers and are primarily found over sandy substrate in their natural habitat. During the rainy season, rainbow sharks migrate to floodplains and flooded forests, and then return to the rivers as the waters recede.

While these fish are currently listed as ‘Least Concern’ by the IUCN Red List, the population has been declining in the wild. There are several reasons for this decline, including the damming of rivers, wetland drainage, and logging. While the aquarium trade is listed as one of the reasons for declining populations, this seems unlikely, as most rainbow sharks currently available are commercially bred.

Aquarium

Rainbow sharks grow to a fairly large size (6 inches/15 cm) in the home aquarium and become more active as they age. Because of this, an individual shouldn’t be housed in anything smaller than a 30-gallon (110 liters) aquarium.

If two of these fish are going to be kept together, an aquarium of at least 55 gallons (110 liters) should be provided, with a minimum width of 3 feet (approximately 1.0 meters). This should allow each fish to establish a territory, but aggression may still become a problem.

While some people attempt to keep these fish in a community tank, it’s not uncommon for an adult rainbow shark to terrorize an aquarium. This is especially true if a rainbow shark is kept with other bottom-dwelling fish or any other similarly ‘finned’ species, including red-tailed sharks or other rainbow sharks.

Decorations & Lighting

Rainbow sharks should be kept in an aquarium designed to mimic their natural river environment. They should be provided with a soft, sandy substrate, along with smooth river rocks. Small aquatic plants should be placed in the background of their tank, making sure to leave an open swimming area for the fish.

Bogwood, driftwood, and caves should also be added to a rainbow shark aquarium to provide them with numerous hiding places.

Strong lighting is recommended for rainbow shark tanks, as bright light contributes to the growth of algae. While these fish aren’t solely algae eaters, they will continually graze on algae throughout the day.

Filter

Like most riverine species, rainbow sharks are very intolerant of any build-up of waste in their tank. Their aquarium water must be kept as clean as possible, and a strong filter is key in keeping these fish healthy.

One of the best filters to use on a rainbow shark tank is a hang-on-back filter. Not only do these filters provide much-needed current, but if properly maintained, it will keep an aquarium’s water crystal clear.

I personally recommend using an AquaClear Power Filter. I’ve been using Aquaclear Power Filters for years in my aquariums and it does an incredible job at keeping the tanks clean. And the filters rugged design means it should last for years without issue. I’ve had some Aquaclear Power Filters running on aquariums for over ten years and they’re still going strong.

Feeding

Rainbow sharks primarily feed on algae and periphyton (tiny organisms that live on rooted aquatic plants), and small invertebrates in the wild.

Aside from ensuring there is some algae for rainbow sharks to browse on in their aquariums, they should also be offered a diverse diet. Rainbow sharks should be fed frozen food (bloodworms, daphnia, brine shrimp), along with prepared fish food and regular offerings of lightly blanched vegetables (lettuce, zucchini, and shelled peas). Learn How to Feed Vegetables to Aquarium Fish here.

I recommend using a herbivore food for these fish, and one of the best foods you can feed them is Hikari Algae Wafers. This food contains high levels of vegetable matter for algae eaters, and contains spirulina, an excellent source of vitamins and nutrients. And the wafers sink to the bottom, making it a perfect food for rainbow sharks.

Breeding

It’s almost impossible to sex juvenile rainbow sharks, but they can be sexed with some difficultly once they reach adulthood. The females will have a noticeably rounder body than the males, while the males will exhibit a dark edge to their anal fin.

Contrary to what many sources claim, fishkeepers have been breeding rainbow sharks as far back as 1970 (first described by Armstrong in the German aquarium publication, DATZ).

However, while there have been sporadic successes breeding rainbow sharks, the details on how they were bred vary from report to report. There doesn’t seem to be a reliable method to breed rainbow sharks outside of fish farms at this time.

Tank Mates

It’s important to choose the right tank mates for rainbow sharks, as these fish will often display aggression towards certain species of fish. Any similarly finned species should be avoided (i.e. red-tailed sharks) as they will often harass each other until one fish is dead.

While juvenile rainbow sharks can often be housed in the same aquarium, it becomes difficult to keep any of these fish together as they mature. Only the very largest aquariums (55 gallons+) offer any hope of successfully keeping more than a pair of rainbow sharks together, and that’s assuming it contains numerous caves and hiding spots.

Most bottom-dwelling fish should also be avoided in a rainbow shark tank, though there are some reports these fish may co-exist somewhat peacefully with loaches. But this might be more to do with individual fish’s temperament, rather than loaches and rainbow sharks making good tank mates.

The best fish to keep with rainbow sharks are midlevel and top dwelling schooling fish. Some good choices are pearl gouramis, zebra danios, tiger barbs, cherry barbs, harlequin rasboras, and rainbowfish.