Bloodfin Tetra (Aphyocharax anisitsi)

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.

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.

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.