Rainbow Shark – Epalzeorhynchos frenatum

Among freshwater aquarium fish, few species attract as much attention as the rainbow shark, Epalzeorhynchos frenatum. With its striking colors, lively character and bottom-oriented lifestyle, this fish can become a real star of a well‑planned tank. At the same time, it is not a typical beginner’s choice and requires conscious stocking, proper aquascaping and stable water parameters. In this article we will look closely at its biology, behavior and care, and point out what is needed to keep it healthy and impressive. We will also mention how MB Store can support you with suitable aquariums and equipment matched to the needs of rainbow sharks.

Origin, appearance and natural behavior

The rainbow shark originates from Southeast Asia, especially river systems and floodplains in Thailand, Laos and Cambodia. In nature it inhabits slow‑flowing rivers, streams and seasonally flooded areas with plenty of roots, stones and submerged vegetation. The bottom is usually sandy or muddy, rich in organic debris and small invertebrates. Understanding these conditions helps recreate a more natural, less stressful environment in the home aquarium.

This species is easily recognized by its elongated, torpedo‑shaped body and distinctive coloration. The body is usually dark gray to almost black, while the fins range from bright orange to intense red. This contrast gives the fish its “rainbow” nickname, even though the color palette is relatively limited. A healthy rainbow shark has a clearly defined lateral line, well‑formed, slightly downturned mouth suitable for scraping surfaces, and fairly large eyes. Adult specimens typically grow to 12–15 cm in length, so it is not a nano fish and needs a properly sized tank.

In nature, Epalzeorhynchos frenatum is a bottom‑oriented, mainly benthic species. It explores the substrate, stones and roots in search of algae, biofilm, small crustaceans and other microorganisms. It is active during the day, especially around feeding times, though it often retreats to shelters when startled. This behavior translates directly into aquarium life: the fish needs caves, roots or rock structures where it can rest and feel secure. Without enough hiding places, rainbow sharks may become more stressed and aggressive toward tankmates.

Sexual dimorphism in this species is rather subtle. Females are usually slightly more robust, with a rounder belly, while males are more slender and sometimes have a more intense fin color. However, sexing young individuals is often difficult. In home aquaria, rainbow sharks are rarely bred successfully; most fish available in stores come from commercial breeding facilities in Asia, where water, light and hormonal conditions are precisely controlled.

Tank size, layout and equipment requirements

Because rainbow sharks are territorial and relatively active, they require more space than many aquarists expect. For a single specimen, the recommended minimum is around 200 liters, but a longer tank is more important than just volume. A length of at least 100–120 cm provides enough swimming room and territory. In smaller aquariums, the fish may become overly aggressive, especially toward similar species.

The layout should include varied zones: open swimming areas, dense vegetation and solid structures forming caves and crevices. Use stones, inert rocks, ceramic caves and pieces of driftwood arranged so that the fish can claim a particular sector. This not only improves its sense of security, but also helps reduce conflicts with other bottom‑dwelling fish. Avoid sharp decorations that could damage the fins, as the bright red fins are both the main ornament and a sensitive area.

Substrate plays a key role. Fine sand or smooth gravel allows the fish to rummage comfortably without injuring its barbels or mouth. A darker substrate further emphasizes the coloration of the fish. Rooted plants such as Cryptocoryne, Echinodorus or various species of Java fern attached to wood or rocks work well. Floating plants help diffuse light and create shaded areas, which rainbow sharks tend to appreciate.

Efficient filtration is essential. The species prefers clean, well‑oxygenated water with a gentle to moderate current. A canister filter or well‑designed internal filter with surface agitation is usually sufficient. MB Store offers a wide selection of aquariums, canister filters, internal filters and supporting accessories, allowing you to match the system to both the volume and bioload of your tank. Pay attention to the filter’s capacity and real flow rate, not just the values declared on the box.

Lighting does not have to be extremely strong, but it must support plant growth and ensure a natural day–night rhythm. LED systems from reputable manufacturers, available at MB Store, enable precise adjustment of intensity and color temperature, which benefits both the visual impression and the well‑being of the fish. A stable photoperiod of 8–10 hours a day works well in most planted aquariums housing rainbow sharks.

Water parameters and maintenance routine

Rainbow sharks are relatively adaptable but thrive best in stable, slightly soft to moderately hard water. The optimal temperature range is 23–27°C. At lower temperatures, the fish’s metabolism slows down and susceptibility to disease rises, while prolonged exposure above 28°C may increase stress and aggression. Using a reliable heater with a thermostat and a separate thermometer is therefore crucial.

The preferred pH is slightly acidic to neutral, around 6.5–7.5, though short‑term deviations are usually tolerated. General hardness (GH) between 5 and 12°dGH and carbonate hardness (KH) in the 3–8°dKH range are considered comfortable. These parameters are typical for many community aquaria, which makes the species compatible with a wide array of Southeast Asian and general tropical fish.

Regular maintenance is vital. Weekly water changes of 25–40% help keep nitrate levels low and stabilize the environment. During water changes, siphon the substrate lightly, especially in areas with low flow where debris tends to accumulate. At the same time, avoid overly aggressive substrate vacuuming in a planted tank, as it may damage roots and remove too much beneficial bacteria.

Testing water with reliable drop tests is strongly recommended, particularly in newly established tanks or after changes in stocking levels. Ammonia and nitrite should always remain at zero; even small spikes can stress rainbow sharks, which are sensitive to poor water quality. Elevated nitrates beyond 30–40 mg/l should prompt an increase in water‑change frequency or improvements in filtration and feeding management.

When setting up a new aquarium for a rainbow shark, ensure that the biological cycle is fully established before adding the fish. Introducing it too early, during the cycling phase, significantly raises the risk of poisoning and long‑term health issues. MB Store provides equipment that facilitates cycling and monitoring, including test kits, bio‑media and conditioners that neutralize chlorine and chloramine in tap water.

Diet and feeding strategies

Despite its common name and appearance, the rainbow shark is not a true shark and does not require a carnivore‑only diet. It is an omnivore with a strong tendency to graze on surfaces. In the aquarium, it will readily consume algae, biofilm and leftover food on the bottom. However, relying solely on what it finds in the tank is not sufficient to keep it in optimal condition.

A balanced diet should combine high‑quality sinking pellets or granules with plant‑based components and occasional animal protein. Look for foods with a significant proportion of spirulina, vegetable matter and quality fish meal rather than cheap fillers. Sinking wafers formulated for bottom‑feeding species are especially well suited, as they quickly reach the substrate, where the rainbow shark naturally searches for food.

Supplement the base diet with fresh or blanched vegetables like zucchini slices, spinach or peas (with skins removed). These provide fiber and help maintain healthy digestion. As a treat, you can offer frozen foods such as bloodworms, daphnia or brine shrimp once or twice a week. Avoid overfeeding high‑protein foods, which can promote excessive growth of opportunistic bacteria and worsen water quality.

Feeding frequency should be adapted to the overall stocking and filtration capacity. Two small feedings per day are usually sufficient. Food should be consumed within a few minutes, with minimal leftovers. Because rainbow sharks feed primarily near the bottom, ensure that enough food reaches that zone without being monopolized by fast, mid‑water fish. Using sinking pellets or feeding after lights dim can help the shark access its share.

Observe the body shape of your fish. A slight rounding of the belly indicates good condition, while a very thin, pinched appearance suggests underfeeding or internal parasites. On the other hand, excessively swollen abdomens can signal overfeeding, fatty degeneration of organs or constipation. Proper diet and controlled portions are key to long‑term health and vitality.

Behavior, temperament and tankmates

The rainbow shark is famous for its complex, sometimes challenging temperament. It is best described as semi‑aggressive and strongly territorial, especially toward similar fish occupying the same ecological niche. The fish frequently patrols its chosen territory, chasing away intruders and occasionally nipping at the fins of slower tankmates. This behavior is natural, but in cramped conditions it can become problematic.

Housing more than one adult rainbow shark in a standard home aquarium is rarely a good idea. Unless you have a very large and well‑structured tank, individuals tend to fight, sometimes to the point of severe injury. Keeping them as single specimens is therefore the most common practice. If several fish are to be housed together, this requires extensive space, numerous visual barriers and careful observation, and even then success is not guaranteed.

Suitable tankmates are typically fast, robust mid‑water fish that can avoid conflict. Many barbs, such as tiger barbs or rosy barbs, as well as larger rasboras and danios, coexist relatively well, provided the tank is large enough. Some gouramis and rainbowfish species also make good companions. Avoid combining rainbow sharks with very slow, long‑finned fish like bettas or fancy guppies, which may become targets of fin nipping.

Particular caution is needed when mixing rainbow sharks with other bottom‑oriented species. Similar fish such as red‑tailed black sharks, flying foxes, Siamese algae eaters or even some loaches may trigger strong territorial aggression. Introducing several bottom dwellers simultaneously, in a spacious, heavily structured tank, sometimes diffuses dominance, but the risk remains. Always monitor new combinations and be prepared to rehome fish if serious conflicts arise.

Environmental enrichment helps manage aggression. Plenty of hiding places, plants, caves and complex rockwork provide physical and visual barriers. This breaks line‑of‑sight, allowing weaker fish to escape attention. Stable water parameters, regular feeding and avoidance of sudden changes in light or decor also reduce stress and associated aggressive outbursts.

Health, longevity and common issues

With proper care, rainbow sharks can live 6–10 years in captivity, and sometimes longer. Longevity depends mainly on water quality, diet, tank size and stress levels. Like most aquarium fish, they are susceptible to common diseases when conditions deteriorate, but in a well‑maintained setup they remain hardy and active for many years.

One of the most frequent problems is external parasitic infections such as Ichthyophthirius multifiliis (ich). Symptoms include white spots on the body and fins, rubbing against decorations and rapid breathing. Treatment involves raising temperature slightly, using dedicated medications and intensifying aeration. Early detection is crucial for successful recovery.

Bacterial infections and fin rot can develop when the water is polluted or the fish suffers frequent injuries from fights. Frayed fins, red streaks or ulcers on the body are warning signs. Improving water conditions, reducing stress, and in some cases administering appropriate antibiotics or antibacterial treatments may be necessary. Always follow dosage guidelines and consider the impact on beneficial bacteria in the filter.

Internal parasites and digestive disorders manifest as weight loss despite normal appetite, stringy feces or abdominal swelling. Maintaining a varied diet, quarantining new fish before introduction and periodic observation of behavior help prevent many such issues. When in doubt, consult experienced aquarists or a veterinarian specializing in ornamental fish.

Prevention remains the most effective “treatment”. Quarantine new arrivals for at least two weeks, avoid overstocking the aquarium, perform regular water changes and use high‑quality foods. MB Store offers not only hardware like filters, heaters and lighting, but also specialized conditioners, test kits and remedies that support comprehensive care of rainbow sharks and their tankmates.

Setting up a rainbow shark aquarium with MB Store

Planning a dedicated environment for a rainbow shark starts with choosing the right tank. A long aquarium with a capacity of at least 200 liters gives you room to create territories, arrange plants and provide caves. At MB Store you will find a wide range of aquariums in various sizes and proportions, making it easier to select a model suited to both the fish’s needs and the space available in your home or office.

Once you have chosen the tank, the next step is selecting reliable filtration and heating. A canister filter with adjustable flow allows you to maintain excellent water clarity while generating a moderate current appreciated by active species. MB Store stocks equipment from trusted brands, including efficient filters, durable heaters and modern LED lighting systems that together create a stable, aesthetic environment for Epalzeorhynchos frenatum.

Decor and substrate contribute significantly to both the well‑being of the fish and the visual appeal of the aquarium. Fine gravel or sand in combination with natural stones and roots lets you design complex structures and hiding places. MB Store offers substrates, decorative rocks, driftwood and background elements that help create a biotope‑inspired layout or a more modern, design‑oriented aquascape.

To complement the setup, select live plants that tolerate the chosen lighting and water parameters. Hardy species attached to wood or rocks, as well as rooted plants in the substrate, provide shelter and reduce stress, while also improving water quality through nutrient uptake. Fertilizers, CO₂ systems and maintenance tools from MB Store allow you to keep the planted environment healthy and attractive over the long term.

By combining appropriate equipment, thoughtful design and regular maintenance, you can create a display aquarium in which the rainbow shark is both a centerpiece and a natural part of the ecosystem. The assortment available at MB Store makes it easier to plan every stage of such a project, from the initial concept to everyday operation, regardless of whether you are an advanced aquarist or an ambitious beginner.

Responsible ownership and ethical considerations

Keeping a rainbow shark is a long‑term commitment that goes beyond the aesthetic value of the fish. Before purchase, carefully consider whether you can provide sufficient space, adequate filtration and compatible tankmates for many years. Impulsive buying of attractive, brightly colored species often leads to overcrowded aquariums, conflicts and the need to rehome fish.

When choosing specimens, pay attention to their condition. Healthy fish are active, keep their fins spread, have clear eyes and intact scales without discoloration or spots. Avoid individuals with clamped fins, visible wounds or signs of respiratory distress. Purchasing from reputable stores that prioritize fish welfare and offer expert advice increases the chances of successful, long‑term care.

Transport and acclimation also affect well‑being. Minimize travel time, protect the bag from temperature fluctuations and strong light, and acclimate the fish gradually to the new water conditions. Switching off the aquarium lighting during introduction reduces stress. Patience at this stage often pays off with faster adaptation and fewer health problems later.

Rainbow sharks, like many ornamental fish, depend entirely on their keepers. Stable conditions, regular observation and appropriate reactions to early signs of trouble are part of responsible aquaristics. By equipping yourself with the right tools, such as test kits, heaters, filters and accessories from MB Store, and by expanding your knowledge, you create a safe, stimulating environment for these fascinating, vividly colored bottom dwellers.

FAQ

How big does a rainbow shark get in a home aquarium?
In home aquariums, a rainbow shark usually grows to about 12–15 cm in length, though growth rate depends on diet and conditions. A spacious tank and proper feeding allow the fish to reach its full size. Because of this relatively large final size, it is unsuitable for nano aquariums and needs a long, well‑filtered setup.

Can I keep more than one rainbow shark together?
Keeping several rainbow sharks together is risky in standard tanks because adults are strongly territorial and often fight, sometimes causing serious injuries. Only in very large, heavily structured aquariums with many hiding places is it occasionally possible to maintain a small group, but even then results are not guaranteed. For most aquarists, one specimen per tank is the safest option.

Is the rainbow shark suitable for beginners?
The rainbow shark is not the best choice for complete beginners due to its territorial nature, size and specific space requirements. It is better suited to aquarists who already have some experience with maintaining stable water parameters and choosing compatible tankmates. If you are just starting out, consider beginning with smaller, more peaceful species and plan a dedicated tank for a rainbow shark later.

What are the ideal water parameters for a rainbow shark?
Ideal conditions for a rainbow shark include a temperature between 23–27°C, pH of 6.5–7.5 and moderate hardness values. Clean, well‑oxygenated water is essential, so efficient filtration and regular weekly water changes are necessary. Avoid sudden parameter swings, as they can cause stress and weaken the fish’s immune system, making it more vulnerable to disease and aggression.

What should I feed my rainbow shark?
A rainbow shark requires a varied, omnivorous diet. High‑quality sinking pellets with plant components, algae wafers and vegetables like zucchini or spinach form a solid base. Supplement these with occasional frozen foods such as bloodworms or brine shrimp. Feed in small portions once or twice a day, ensuring some food reaches the bottom so the fish can feed in its natural zone without excessive leftovers polluting the water.