Flying Fox Fish Overview
The flying fox (Epalzeorhynchos kalopterus) is a slender, active freshwater fish in the carp and minnow family (Cyprinidae). It comes from Southeast Asia, with sources naming areas such as Borneo, Java, Sumatra, Thailand, and Malaysia, where it lives in flowing streams with rocky and sandy bottoms. Aquarists keep it mainly for its appetite for green algae and its busy swimming, and it spends most of its time near the bottom and middle of the tank.
How Big Do Flying Foxes Get?
Reported sizes vary a little between sources, but adult flying foxes are commonly given at around 5.5 to 6.5 inches (14 to 17 cm) in aquaria. Many sold in stores are juveniles and look much smaller. With good care, a lifespan of several years is expected, and some sources cite up to around eight.
Are Flying Foxes the Same as Siamese Algae Eaters?
No, but they look similar, and the two are often confused or mislabeled in stores.
- Flying fox (Epalzeorhynchos kalopterus): a slim body with a dark stripe and a thin golden line above it, plus a pointed face with small barbels.
- Siamese algae eater (Crossocheilus oblongus): a similar torpedo shape, with a bold black line along the body and clear fins. Aquarium Co-Op describes it as around 6 inches as well.
- Chinese algae eater: a different fish with a suckermouth that can grow much larger, and is generally regarded as a poor community fish.
If algae control is your main goal, look closely at the stripe pattern and ask the store which species you are buying. Our overview of the best aquascaping fish also discusses algae eaters for planted tanks.
Tank Setup and Size
Recommendations on tank size vary. A common view is that a flying fox needs a good-sized tank with a long footprint, with 30 gallons or more often suggested for one fish and considerably larger tanks for groups. One retailer lists 50 gallons for a single adult and 120 gallons or more for a group. The safer approach is to size up, since they are active swimmers.
Good setup elements include:
- Rocks, driftwood, and caves, to give territories and hiding spots.
- Plenty of plants, which flying foxes are generally said not to eat.
- Moderate to strong flow, mimicking stream conditions.
- A secure lid, because they can jump.
Water Parameters
Reported ranges differ slightly. A commonly cited range is about 72 to 79°F (22 to 26°C), with a pH around 6.0 to 7.5. They are often described as hardy, but stable, clean, well-oxygenated water is important.
Diet
Flying foxes graze on algae and biofilm but should not be expected to survive on algae alone. Offer a varied diet:
- Algae wafers or spirulina-based foods.
- Blanched vegetables, such as zucchini or cucumber.
- Good quality flake, pellets, and occasional frozen or live foods.
Adult flying foxes are said to prefer plant-based foods, so keep the diet mostly vegetable-based. Their appetite for algae typically fades with age, and they may ignore certain algae types.
Are Flying Foxes Aggressive?
They are generally peaceful toward dissimilar fish when young, but they can become territorial as they mature, especially with their own kind or similar-looking bottom fish. Some retailers note a hierarchy forms within groups, and stress and aggression are more likely with small groups in crowded tanks. For this reason, many keepers prefer to keep a single flying fox, or a larger group in a very large tank. See our aggressive freshwater fish guide for how to think about this kind of territorial behavior.
Good Tankmates
Larger peaceful, quick-moving community fish are generally the best fit. Examples that keepers commonly suggest include medium-sized tetras, rasboras, danios, and barbs. Avoid very shy, slow, or tiny fish, which can be outcompeted or harassed. Calm, shy species such as the spike-tailed paradise fish are usually a poor match for a boisterous flying fox.
Sexing and Breeding
Males and females look nearly identical, so sexing is difficult. Successful breeding in home aquariums is described as essentially undocumented, so do not plan on breeding them.
Is It the Hardest Fish to Keep Alive?
No. Flying foxes are usually described as fairly hardy. Common problems come from small tanks, poor-quality or mislabeled stock, and aggression rather than inherent fragility. Which fish are “hardest” to keep varies with experience; delicate wild-caught species and some marine fish are more often cited.
Frequently Asked Questions
Is a flying fox a good beginner fish? It can be, but its adult size and territorial nature make it better for those with a larger tank.
Can flying foxes live alone? Yes. Because they can be territorial with each other, a single fish is a common choice.
Will they clean my tank? They graze algae, but they are not a replacement for maintenance and water changes. If algae is getting out of hand, see our guide to killing algae in a fish tank safely.