Epalzeorhynchos bicolor

The Red-tailed Shark is a popular cyprinid from Asia that commands attention, not just for its appearance, but for its dynamic and often challenging behavior. Inhabiting rivers and streams in its natural environment, it appreciates a well-oxygenated aquarium with a moderate level of water movement. Providing a spacious tank is non-negotiable, as this fish grows to a considerable size and establishes a distinct territory that it will vigorously defend. The aquascape should be rich with hiding places such as rock caves, driftwood, and dense plantings. These structures serve as visual barriers and defined territories, which can help mitigate stress and aggression.

Its social behavior is a critical aspect of its care. This species is solitary and highly territorial, especially towards its own kind and other fish with a similar body shape or coloration. Housing more than one can lead to relentless chasing and fighting unless they are kept in a very large aquarium in a specific minimum group size to diffuse aggression, a difficult setup that is best left to experienced aquarists. For most community tanks, a single individual is the recommended approach. Ideal tank mates are robust, fast-moving fish that occupy the upper water column and have a different appearance, such as larger tetras, danios, or barbs. Slow-moving, long-finned fish should be avoided.

As an omnivore, its dietary needs are straightforward. A high-quality sinking pellet or wafer should form the basis of its diet, ensuring food reaches its bottom-dwelling domain. This should be supplemented with various foods including frozen or live options like bloodworms and brine shrimp, as well as vegetable matter such as blanched zucchini or spinach. They are also known to graze on biofilm and algae within the aquarium, contributing to the tank's maintenance. Due to its critically endangered status in the wild, the specimens available in the hobby are commercially bred, making their responsible care in aquaria an important part of the species' continued presence.

Epalzeorhynchos bicolor is a freshwater fish belonging to the family Cyprinidae, the largest family of freshwater fishes. Its classification places it among carps and minnows, not elasmobranchs, despite its common name. The species is endemic to river systems in Asia, although its wild populations are under extreme threat.

Morphologically, E. bicolor exhibits a fusiform body shape, which is streamlined and laterally compressed, an adaptation for maneuvering in moderate currents. This body plan facilitates its active, fast-swimming behavior observed both in nature and captivity. It is primarily a benthic and mid-water dweller, a niche supported by its anatomy.

Ecologically, the species functions as an omnivore with a diet that includes aufwuchs, plant matter, and small invertebrates. In an aquarium setting, it is recognized as a biofilm consumer, actively grazing on submerged surfaces. Its metabolism rate, oxygen consumption, and waste production are moderate, resulting in a standard bioload for a fish of its size and activity level. Its social structure is classified as solitary, and it displays significant intraspecific territoriality. This agonistic behavior is a key survival trait related to resource defense in its natural habitat, which is crucial to consider for ex-situ management in aquariums.

The most significant scientific aspect of E. bicolor is its conservation status. It is listed as Critically Endangered on the IUCN Red List of Threatened Species due to habitat degradation, pollution, and dam construction in its native range, which have led to a catastrophic decline in wild populations. Consequently, the global aquarium population is sustained entirely through aquaculture, often involving hormonal induction for commercial-scale breeding. This makes the aquarium hobby a vital reservoir for the species, albeit disconnected from its natural ecosystem.

Successfully breeding the Red-tailed Shark in a home aquarium is an exceptionally rare and difficult achievement, with most specimens in the hobby being products of large-scale commercial breeding farms. These operations typically rely on hormonal injections to induce spawning, a method that is not practical or accessible for the average aquarist. The species has specific reproductive requirements that are challenging to replicate.

For any dedicated attempt, sexing the fish is the first, albeit subtle, step. Sexual dimorphism is not pronounced. Generally, mature females may appear slightly larger and have a rounder, fuller abdomen compared to the more slender males. Males may also exhibit more intense coloration, but this can be an unreliable indicator. It is often best to acquire a group of juveniles and allow them to grow to maturity to observe potential pairing or group dynamics.

As egg-scatterers, they do not provide parental care and will predate their own eggs and fry. A dedicated, very large breeding aquarium is essential. This tank should be equipped with a soft, acidic water profile and structures to serve as spawning sites, such as fine-leaved plants like Java moss or synthetic spawning mops. Conditioning a potential breeding group with a diet rich in live and frozen foods for several weeks is critical to promote gamete development. Simulating natural environmental triggers, such as performing a large water change with slightly cooler, softer water to mimic a rainy season, may help encourage spawning behavior. If spawning occurs, it is a vigorous event, after which the adults must be removed immediately. The adhesive eggs will hatch within a few days. The newly hatched fry will first consume their yolk sacs. Once free-swimming, they must be fed microscopic foods like infusoria or liquid fry food. As they grow, their diet can be transitioned to baby brine shrimp and finely crushed flakes. Maintaining immaculate water quality is paramount for the survival of the sensitive fry.