Epalzeorhynchos kalopterus

The Flying Fox is an active, torpedo-shaped fish from Southeast Asia, known for its busy nature and appetite for algae, making it a dynamic bottom-dweller. This fish is constantly on the move, exploring the lower and middle regions of the aquarium as it forages for food. Its diet is varied, and while it's an excellent consumer of biofilm and certain types of algae, it's not a picky eater and will readily accept a wide range of commercially prepared foods like flakes, pellets, and wafers. This species thrives in an environment with noticeable water movement, which mimics the streams of its natural habitat.

While energetic and interesting to watch, the Flying Fox develops a territorial personality as it matures. It can become aggressive towards its own kind and other fish with a similar body shape or habits. For this reason, it is generally recommended to keep only one in a community aquarium to maintain a peaceful environment. Due to its active swimming habits and potential size, it requires a spacious tank with plenty of room to roam. A secure lid is also a wise precaution, as its speed can sometimes lead to it jumping.

Native to the river basins of Southeast Asia, the Flying Fox inhabits clear, fast-flowing streams and rivers with sandy or rocky substrates. These environments are typically rich in oxygen and feature submerged driftwood, stones, and dense plant life, which are all covered in a layer of biofilm and algae that forms a primary part of its diet. Replicating this habitat is key to its well-being in captivity. An aquarium should be generously sized, with a layout that provides a long, open swimming area. Incorporating smooth rocks, driftwood, and robust plants creates a naturalistic setting, offers grazing surfaces, and establishes territories that can help diffuse aggression.

This species is an omnivore with a voracious appetite. In its natural environment, it continuously grazes on algae and the microorganisms within biofilm. In an aquarium, this grazing behavior should be supplemented with a high-quality, varied diet. Sinking pellets, wafers, and gel foods are excellent staples, but its diet should also include frozen or live foods for protein, and blanched vegetables like zucchini or cucumber to satisfy its herbivorous side. Daily feeding is sufficient for this active fish.

Behaviorally, the Flying Fox is a study in contrasts. As a juvenile, it can be relatively peaceful, but with age, it becomes increasingly territorial and solitary. It is particularly intolerant of its own species and will harass other fish that it perceives as competitors, especially those with a similar shape or that occupy the bottom-dwelling niche. Therefore, keeping a single specimen is the most common and successful approach for a community tank. Suitable tank mates include robust, fast-moving fish that primarily occupy the middle to upper water column, such as larger tetras, barbs, or danios. Slow-moving or long-finned fish should be avoided. A well-maintained environment with strong filtration to ensure clean, well-oxygenated water with medium flow will allow this dynamic fish to thrive.

Epalzeorhynchos kalopterus, a member of the family Cyprinidae, is a freshwater fish native to Southeast Asia. Its taxonomic classification places it within a genus known for active, often territorial, benthic and semi-pelagic species. The morphology of E. kalopterus is highly adapted to its riverine ecological niche. It possesses a fusiform, or torpedo-shaped, body plan which is hydrodynamically efficient, enabling swift movement in habitats with moderate to strong water currents. This body shape, coupled with its active nature, contributes to a medium rate of oxygen consumption, necessitating a well-aerated aquatic environment.

Its ecological role in the wild is primarily that of a grazer. Its sub-terminal mouth is suited for scraping biofilm, periphyton, and algae from various submerged surfaces like rocks, wood, and substrate. This feeding behavior classifies it as a 'biofilm consumer,' playing a role in the primary consumption and nutrient cycling within its ecosystem. As an omnivore, its diet is not strictly limited to plant and algal matter but also includes small crustaceans, insect larvae, and zooplankton found within the biofilm. In a captive setting, its relatively high activity level and medium metabolic rate require a diet that balances vegetable matter with protein to maintain its health and energy.

The species exhibits a notable ontogenetic shift in social behavior, transitioning from a more gregarious juvenile stage to a highly territorial and solitary adult. This intraspecific aggression, along with interspecific aggression towards morphologically similar species, is a significant behavioral characteristic. Its reproductive strategy involves external fertilization as an egg-scatterer, with breeding in captivity being exceedingly rare without hormonal induction, a trait common among many commercially farmed cyprinids. According to the IUCN Red List, E. kalopterus is currently categorized as Least Concern (LC), indicating a stable wild population.

Successfully breeding the Flying Fox in a home aquarium is considered extremely difficult and is a rare accomplishment. Commercial breeding operations rely on the use of hormones to induce spawning, as this species does not readily reproduce under typical captive conditions. This difficulty stems from the challenge of replicating the specific environmental triggers and social conditions required for them to spawn naturally.

Sexing individuals is challenging, as there are no pronounced, reliable external differences between males and females. However, as with many cyprinids, a mature, gravid female may appear noticeably plumper and more rounded in the abdominal region when viewed from above compared to a more slender male. This is often the only subtle clue available to the aquarist.

As an egg-scattering member of the Cyprinidae family, this fish provides no parental care. In a hypothetical breeding scenario designed to mimic nature, a very large, dedicated aquarium would be required. The setup would need to simulate seasonal changes, which often act as spawning triggers. This could involve manipulating water temperature and chemistry, along with increasing water flow to imitate a rainy season. The tank would need to be furnished with appropriate spawning media, such as dense clumps of fine-leaved plants like Java moss or artificial spawning mops, where the fish could scatter their adhesive eggs.

If spawning were to occur, the adult fish must be removed immediately to prevent them from consuming the eggs. The eggs would likely hatch within a couple of days. The newly hatched fry would survive on their yolk sacs for a short period before becoming free-swimming. At that stage, they would require microscopic foods like infusoria, rotifers, or liquid fry food. As they grow, their diet can be transitioned to larger foods such as microworms and newly hatched brine shrimp. Given the lack of documented home breeding successes, any attempt should be considered highly experimental.