Species Overview
The Bloodfin Tetra (Aphyocharax anisitsi) is a classic South American characin that has been a staple of the aquarium hobby for over a century. First described by Eigenmann and Kennedy in 1903 from specimens collected near Asunción, Paraguay, this species has earned a reputation as one of the most forgiving, long-lived, and undemanding tetras available to aquarists of all experience levels. Its understated beauty—a sleek, semi-translucent silver body accented by vivid blood-red fins—develops and deepens with age, making it a slow-burn species that rewards patient keepers with increasingly spectacular displays.
Native to the Paraná, Paraguay, and Uruguay river drainages of southern South America, Bloodfin Tetras inhabit subtropical river basins that experience seasonal temperature fluctuations, including cool winters. This natural exposure to variable conditions has endowed them with an exceptionally wide tolerance for water parameters that few other tetras can match. They can thrive in unheated tanks, tolerate pH swings from acidic to alkaline, and adapt to soft or moderately hard water with equal ease. It is this remarkable adaptability, combined with a lifespan that rivals many cichlids, that makes the Bloodfin Tetra a genuinely exceptional community fish.
Visual Identification
Bloodfin Tetras possess a streamlined, slightly elongated body that is more slender and athletic than many other common tetras. The base coloration is a polished silvery-blue with a subtle iridescent sheen that catches light as they swim. The body is semi-translucent, allowing the backbone and internal organs to be faintly visible—an adaptation that contributes to their common name of Glass Bloodfin. The signature feature, and the source of their common name, is the vivid blood-red coloration of the anal, pelvic, and caudal fins. The dorsal fin often shows red tinting as well, particularly in mature, well-conditioned specimens. When healthy and settled, the contrast between the silver body and deep red fins is genuinely striking.
Sexual Dimorphism
Males are noticeably slimmer and more streamlined than females, with slightly more intense red coloration in the fins. The most reliable identifier comes at maturity: males develop tiny hook-like structures on the rays of their pelvic and anal fins—a unique characteristic among commonly kept tetras. Females are fuller-bodied, especially when carrying eggs, and show slightly less vivid fin color. The two sexes are easily distinguishable when preparing to spawn, as males intensify in color while females become noticeably rounder.
Behavioral Highlights
Bloodfin Tetras are active, fast-swimming fish that occupy the middle and upper water columns. When maintained in proper schools of 8 or more, they engage in tight, synchronized schooling behavior that is mesmerizing to watch. They move as a cohesive unit, rapidly darting across the tank in unison before suddenly changing direction as one. This tight schooling is both a defense mechanism and a social behavior that reduces stress and encourages full color display. They are diurnal and most active during morning and evening feeding times.
Housing Requirements
Bloodfin Tetras are active, fast swimmers that require horizontal swimming space rather than vertical height. The absolute minimum tank size for a school of 6-8 individuals is 20 gallons (76 liters) with a footprint of at least 30 x 12 inches (75 x 30 cm). A 20-gallon long tank is ideal, providing the length these fish need for their characteristic rapid darting behavior. For schools of 10-12 or more, upgrade to 30-40 gallons (114-151 liters) to accommodate their active nature and reduce competition for swimming lanes.
Tank Dimensions and Layout
Long tanks significantly outperform tall tanks for this species. Bloodfins are horizontal swimmers that patrol the length of the aquarium in tight formation. Tank length should be at least 30 inches (75 cm) for a standard school, with 36-48 inches (90-120 cm) being ideal for larger groups. Tank height of 12-16 inches (30-40 cm) is sufficient. A secure, tight-fitting lid is mandatory—Bloodfin Tetras are accomplished jumpers and will exploit any gap in canopy coverage, especially when startled or during feeding frenzies.
Filtration and Water Flow
A reliable hang-on-back filter or canister filter rated for the tank volume is sufficient. Bloodfins prefer gentle to moderate water flow that mimics their native riverine habitats. Moderate flow keeps the water well-oxygenated and distributes food throughout the tank, but strong currents exhaust these active swimmers and disrupt their tight schooling behavior. Position filter returns to create gentle circulation rather than strong directional flow. A sponge filter can be added as supplemental biological filtration and gentle aeration.
Substrate and Hardscape
Dark substrate is strongly recommended. Black sand, dark gravel, or river sand enhances the contrast of their silver bodies and makes the blood-red fin coloration pop dramatically. Light-colored substrate washes out their colors and makes them appear dull. Smooth gravel or sand is preferable to sharp-edged substrate, as these active fish occasionally graze along the bottom. Driftwood and rocks can be added for visual interest and to create broken sightlines that encourage more confident schooling behavior.
Plant Requirements
Live plants are highly beneficial and Bloodfins are completely plant-safe. They do not eat vegetation, unlike their close relative the Buenos Aires tetra. Use a combination of:
- Floating plants: Water sprite, red root floaters, or frogbit to diffuse lighting and reduce skittishness
- Background plants: Amazon sword, Vallisneria, and Cryptocoryne for cover and water quality improvement
- Mid-ground plants: Java fern, Anubias, and Java moss attached to driftwood or rocks
Ensure open swimming lanes in the center of the tank remain unobstructed. Dense planting along the back and sides with a clear center channel is the ideal layout for this active species.
Perform 20% water changes weekly using temperature-matched, dechlorinated water. In heavily stocked community setups, increase to 25% weekly. Bloodfins are hardy and tolerate standard maintenance routines, but consistent water quality is the key to unlocking their exceptional lifespan potential. Fish in tanks with irregular maintenance and elevated nitrates rarely exceed 3-4 years, while those in pristine conditions routinely reach 7-10 years. Never change more than 30% at once to avoid parameter swings. Use a gravel vacuum gently to remove detritus without disturbing plant roots.
Dietary Requirements
Bloodfin Tetras are opportunistic omnivores and surface feeders. In their natural habitat, they consume insect larvae, zooplankton, small crustaceans, and some plant matter in lagoon settings. In captivity, they are famously unfussy eaters that will accept virtually any food offered. However, a varied, high-quality diet is essential for developing and maintaining their vivid fin coloration and achieving their exceptional lifespan potential.
Nutritional Composition
Target a diet comprising approximately 40% protein, 10% fat, and 50% plant matter. High protein levels maintain the vibrant red fin coloration and support their active metabolism. Plant matter provides essential fiber and vitamins. Because they are surface feeders, foods that float or sink slowly are most readily accepted.
Recommended Foods
- Primary dry foods: High-quality tropical flakes or micro-pellets that float on the surface. Bloodfins are surface feeders and prefer foods that remain in the upper water column. Choose flakes high in crude protein for optimal coloration.
- Live foods: Brine shrimp, bloodworms, mosquito larvae, and daphnia. These provide essential proteins and trigger natural hunting behavior.
- Frozen options: Frozen brine shrimp, bloodworms, daphnia, and cyclops—thaw and rinse before feeding.
- Vegetable matter: Spirulina flakes or blanched spinach offered twice weekly. While not primarily herbivorous, they benefit from the vitamins and fiber.
Feeding Schedule
Feed small portions 2-3 times daily. Each feeding should be consumed within 2-3 minutes. Bloodfins are enthusiastic eaters and will quickly consume floating flakes from the surface. Remove uneaten food to prevent ammonia spikes and algae growth. Because they are surface feeders, ensure food is presented at the water surface or allowed to sink slowly. Sinking pellets that drop immediately to the substrate may be missed.
Expert Tip: Color Development
The blood-red fin coloration develops and deepens with age and diet quality. Fish fed exclusively on basic flakes show noticeably duller fin color within 4-6 weeks. Supplementing with carotenoid-rich foods such as spirulina, krill, and high-quality protein sources significantly enhances the intensity of the red pigmentation. By year 3 or 4, well-fed specimens display a depth of color that rivals much more expensive tetra species.
Behavior and Temperament
Bloodfin Tetras are unequivocally peaceful schooling fish that thrive in tranquil community aquariums. Their social structure revolves around tight, synchronized swimming within the school. They are not territorial and pose no threat to other peaceful species. However, they are active, fast swimmers that can intimidate slower, more docile tank mates and may nip at long, flowing fins if their school is too small or if they are kept with inappropriate companions.
Schooling Dynamics
Maintain a minimum of 8 individuals, with an optimal group size of 10-12. In smaller groups, they become skittish, lose color, and redirect their energy into fin-nipping other fish. Bloodfins are among the tightest schoolers in the aquarium hobby—when kept in adequate numbers, they move as a single cohesive unit, rapidly darting across the tank in perfect synchronization. This behavior is both a defense mechanism and a social display that reduces individual stress and encourages full color development.
Fin-Nipping Tendency
While generally peaceful, Bloodfin Tetras have a documented tendency to nip at long, flowing fins. This behavior is most pronounced when: (1) the school is too small (under 6 individuals), (2) they are kept with slow-moving, long-finned fish like bettas or angelfish, or (3) they are bored in a sparsely decorated tank. In a proper school of 8+ with appropriate tank mates, fin-nipping is minimal to nonexistent. The energy that would be directed toward nipping is instead channeled into the tight schooling display.
Activity Patterns
These fish are strictly diurnal and most active during morning and evening hours, coinciding with their natural feeding periods. They occupy the middle and upper water columns almost exclusively, rarely venturing to the substrate. Their constant, rapid swimming patterns create significant movement in the aquarium. They are surface feeders and will eagerly rush to the top of the tank at feeding time.
Tank Mate Selection
Select peaceful, active species of similar size that do not have long, flowing fins. Ideal companions include:
- Other tetras such as Cardinal Tetra, Ember Tetra, Glowlight Tetra, and Black Skirt Tetra
- Rasboras such as Harlequin Rasbora and Chili Rasbora
- Danios and White Cloud Mountain Minnows—excellent cold-water companions for unheated setups
- Rainbowfish species that share similar water parameter preferences
- Corydoras catfish—peaceful bottom-dwellers that occupy different tank zones
- Small Loricariids such as Otocinclus and Bristlenose Pleco
- Livebearers such as Platies and Swordtails (avoid fancy Guppies due to fin-nipping risk)
- Dwarf cichlids such as Apistogramma and Ram Cichlids
- Freshwater shrimp (Neocaridina, Caridina) and snails (Nerite, Ramshorn, Mystery)
Never house with: Betta fish (fin nipping), Angelfish (fin nipping and stress), fancy Guppies (fin nipping), slow-moving fish like Discus (outcompeted and stressed), large or aggressive cichlids, Goldfish (temperature and temperament mismatch), or any predatory species large enough to eat them. Avoid keeping with the closely related Buenos Aires Tetra, which is much more boisterous and may outcompete Bloodfins.
Spawning Behavior
Bloodfin Tetras are relatively easy to breed and make an excellent first breeding project for aspiring aquarists. Spawning typically occurs in the morning, often triggered by a gradual increase in light intensity that simulates dawn. The male intensifies his coloration and pursues the female, nudging her toward fine-leaved plants or a spawning mop. The female releases 300-500 eggs that are only slightly adhesive—many fall to the substrate or float to the surface. The eggs are clear and approximately 1 mm in diameter. Parents must be removed immediately after spawning, as they will readily consume eggs and fry.
Health and Disease Management
Bloodfin Tetras are exceptionally hardy and resistant to disease when maintained in stable aquariums with appropriate water quality. Their wide parameter tolerance and robust constitution make them one of the most disease-resistant tetras available. However, they are not invincible—stress from inadequate schooling numbers, poor water quality, or inappropriate tank mates is the primary trigger for illness. Prevention through proper school size, consistent maintenance, and careful tank mate selection is the best medicine.
Medication Sensitivity and Tolerance
Bloodfin Tetras have a favorable medication profile compared to more sensitive species:
- Copper: Tolerated up to 0.2 mg/L. Standard ich treatments are generally safe at recommended doses.
- Formalin: Tolerated at standard doses for external parasites.
- Malachite Green: Sensitive to high doses; use at half-strength to prevent gill irritation.
- Aquarium Salt: Tolerated up to 5 ppt (parts per thousand) for short-term therapeutic baths. Standard salt treatments of 1 tablespoon per 5 gallons are safe for this species.
- Safe Options: Praziquantel for internal parasites and flukes, Methylene Blue for fungal issues, Kanamycin and Erythromycin for bacterial infections, and broad-spectrum antibiotics mixed into food for fin rot.
Quarantine Protocol
Quarantine all new Bloodfin Tetras for a minimum of 2-3 weeks in a separate 10-gallon (38 liter) tank with a mature sponge filter. Observe for feeding response, fin condition, and signs of ich or velvet. While hardy, newly imported fish may carry parasites from wholesale systems. Standard drip acclimation over 30-45 minutes is sufficient for this adaptable species.
Breeding Bloodfin Tetras
Bloodfin Tetras are relatively easy to breed and make an excellent first breeding project for aspiring aquarists. They are egg scatterers that spawn readily with minimal conditioning, producing large numbers of eggs that hatch quickly. The primary challenges are protecting the eggs from parental predation and raising the tiny fry through their delicate first weeks.
Conditioning Breeders
Select 8-10 mature fish at least 9-12 months old. Condition them for 2 weeks in a separate tank with heavy feedings of live blackworms, baby brine shrimp, and high-quality flakes. During conditioning, males will intensify their red fin coloration while females become noticeably plumper and rounder. Sexing is straightforward: males are slimmer with more vivid fins and tiny hook-like structures on the anal and pelvic fin rays; females are fuller-bodied with slightly duller coloration.
Spawning Setup
Prepare a dedicated 10-gallon (38 liter) breeding tank with:
- Water depth of 4-6 inches (10-15 cm) to concentrate fry food
- Soft, slightly acidic water: pH 6.5, 4 dGH (71 ppm), temperature 75°F (24°C)
- A spawning mop made of acrylic yarn or dense Java moss
- Dim lighting—eggs and fry are highly sensitive to bright light
- An air-powered sponge filter set to gentle bubble output
- No substrate for easy cleaning and egg collection
Fill the tank with reverse osmosis or aged tap water treated to the specified parameters. A dark bottom (black paper or dark substrate) makes eggs easier to spot.
Spawning Process
Transfer the conditioned group to the breeding tank in the evening. Simulate dawn the next morning by gradually increasing light intensity over 30 minutes. Spawning typically occurs in the morning hours. The male pursues the female, nudging her toward the spawning mop or fine-leaved plants. The female releases 300-500 slightly adhesive eggs that scatter among the plants, fall to the substrate, or float to the surface. The eggs are clear and approximately 1 mm in diameter. Remove the parents immediately after spawning is observed, as they will consume eggs and fry without hesitation.
Incubation and Hatching
Eggs hatch in 24-30 hours at 75°F (24°C). This is significantly faster than many other tetra species. The newly hatched fry are extremely small, measuring approximately 0.08 inches (2 mm). They will initially cling to surfaces using a sticky secretion on their heads, often attaching to the aquarium glass, plants, or equipment in shaded areas. After 3-5 days, they become free-swimming and begin searching for food. Keep the tank dark for the first 5 days to reduce stress and encourage feeding.
Fry Rearing
Bloodfin Tetra fry grow at a moderate rate compared to other tetras:
- Days 1-3: Feed infusoria and green water. The fry are too small for most commercial foods at this stage.
- Days 3-7: Introduce microworms and vinegar eels. Continue infusoria as a backup.
- Days 7-14: Newly hatched baby brine shrimp (Artemia nauplii) can be introduced. Some fry may not accept them immediately.
- Week 2+: Gradually introduce powdered flake food and crushed high-quality pellets.
Perform daily 10-15% water changes using water from the parents' tank. Use airline tubing to siphon waste without removing fry. By 3-4 weeks, the fry will be large enough to accept standard fry foods. By 2-3 months, they reach 0.75-1 inch (2-2.5 cm) and begin showing juvenile coloration. Sexual maturity is reached at approximately 9-12 months.
easy
Egg-scattering with no parental care. Eggs are only slightly adhesive and scatter among plants, substrate, and water surface. Parents must be removed immediately after spawning to prevent egg predation.
Expert Tips and Common Mistakes
After decades of combined experience with Aphyocharax anisitsi, our editorial team has identified the critical success factors that separate thriving Bloodfin Tetra schools from disappointing attempts. These insights address the specific gaps left by generic care guides and highlight what makes this species truly special.