Costello Tetra

The Costello Tetra, also known as the January Tetra, is a charming small characin native to the Amazon basin. These fish display a subtle iridescent green-gold sheen along their flanks with a distinctive black spot near the gills. Unlike their more colorful relatives like neon tetras, Costello tetras offer a more understated elegance that appeals to aquarists seeking a natural, biotope-style aquarium. They are peaceful schooling fish that should be kept in groups of 6 or more to exhibit their natural behaviors and feel secure. In a well-planted aquarium with soft, acidic water and dim lighting, their metallic highlights become more pronounced. They are active swimmers in the middle water column and make excellent dither fish for shy or newly introduced species.

The Costello Tetra, scientifically known as Hemigrammus hyanuary, represents one of the most elegant yet understated members of the characin family. Named after its discoverer and also commonly called the January Tetra, this species offers aquarists a sophisticated alternative to the more commonly kept neon tetras and cardinal tetras. Their subtle beauty reveals itself through a delicate iridescent green-gold sheen that catches the light as they move through the water, creating a living shimmer that transforms an aquarium into a natural Amazonian stream scene. While they may lack the brilliant red and blue stripes of their famous relatives, Costello Tetras possess a refined charm that has earned them a devoted following among serious aquarists who appreciate natural biotope aesthetics.

Natural Habitat

Costello Tetras are endemic to the vast Amazon River basin, where they inhabit a variety of freshwater environments across Brazil, Peru, and surrounding regions. Their natural range extends throughout the tributaries, flooded forests, and slow-moving streams that characterize this enormous watershed. These fish have adapted to life in warm, acidic waters rich in tannins and organic compounds.

In the wild, Costello Tetras prefer areas with dense vegetation and submerged tree roots that provide shelter and foraging opportunities. They are often found in shallow waters where light filters through the forest canopy, creating dappled illumination that highlights their metallic coloration. The soft, dark waters of their habitat result from decaying leaf litter and botanicals that continuously release tannins.

Water parameters in their natural environment remain relatively stable during the dry season but fluctuate significantly during the annual floods. During flood periods, these fish venture into submerged forest areas to spawn and feed on the abundant food resources available in these temporary aquatic environments. This seasonal adaptability makes them hardy aquarium fish capable of handling minor parameter variations.

The substrate in their native streams typically consists of fine sand, decaying leaves, and organic debris. This soft bottom allows them to forage safely without risk of injury to their delicate barbels and ventral fins. Understanding this habitat helps aquarists recreate appropriate conditions in captivity.

Detailed Tank Setup

Creating an ideal environment for Costello Tetras requires attention to their Amazonian origins and behavioral needs. While a 10-gallon tank represents the absolute minimum for a small group, a 20-gallon long or larger tank provides significantly better conditions for displaying their natural schooling behaviors and reducing stress. The additional swimming space allows the fish to form tighter, more cohesive schools that showcase their coordinated movement patterns.

Planting should be dense and strategic, with tall background plants like Amazon swords, Vallisneria, or Cryptocoryne creating a green backdrop that makes the fish’s metallic sheen visible. Mid-ground plants such as Cryptocoryne wendtii or Cryptocoryne beckettii provide additional structure, while floating plants like Water Sprite, Amazon Frogbit, or Red Root Floaters diffuse overhead lighting and create the dim conditions these fish prefer.

Hardscape elements should include driftwood pieces, which serve multiple purposes. The wood provides hiding spots, creates additional surface area for biofilm growth, and slowly releases tannins that soften water and create the tea-colored conditions Costello Tetras favor. Indian Almond Leaves or other botanicals can supplement this effect while providing additional cover and foraging opportunities.

The substrate should consist of dark gravel or fine sand that mimics the soft bottoms of Amazonian streams. Dark colors enhance the visibility of the fish’s metallic sheen, while soft substrates protect their sensitive undersides during bottom foraging. Avoid sharp or coarse gravel that could damage their delicate fins and barbels.

Lighting should be subdued to moderate, never bright or direct. Use dimmable LED fixtures or place floating plants to filter overhead illumination. The subdued lighting not only brings out the fish’s iridescent colors but also encourages them to display more natural behaviors rather than hiding from bright light.

Water Parameters

Maintaining appropriate water chemistry is essential for Costello Tetra health, coloration, and breeding success. These fish thrive in soft, acidic conditions that mimic their Amazonian homeland, though they demonstrate reasonable adaptability to moderately hard, neutral water in well-maintained aquariums.

Temperature should remain between 72 and 79 degrees Fahrenheit, which corresponds to the warm tropical conditions of their native range. Stability is more important than the exact temperature within this range, so avoid fluctuations greater than 2 degrees over 24 hours. Use a reliable heater with a thermostat to maintain consistent temperatures.

pH levels should ideally fall between 5.5 and 7.0, reflecting the acidic conditions created by decaying botanical matter in their natural streams. While they can adapt to pH levels up to 7.5, their colors and breeding behaviors are most pronounced in softer, more acidic conditions. Peat filtration or the addition of botanicals like Indian Almond Leaves can help maintain appropriate acidity.

Water hardness should remain soft, ideally between 1 and 8 degrees of general hardness (dGH). Hard water can stress these fish and interfere with their osmoregulation. If your tap water is naturally hard, consider using reverse osmosis water blended with tap water to achieve appropriate softness, or collect rainwater where legally permitted.

Ammonia and nitrite must remain at zero at all times, as these compounds are toxic even in small amounts. Nitrate levels should be kept below 20 ppm through regular water changes of 20 to 30 percent weekly. The addition of live plants helps absorb excess nitrates while providing the natural environment these fish prefer.

Diet and Feeding

Costello Tetras are omnivores with a preference for small, protein-rich foods that they would encounter in their natural Amazonian habitats. In the wild, they consume insect larvae, small crustaceans, zooplankton, and plant matter. Replicating this varied diet in captivity ensures optimal health, coloration, and vitality.

High-quality micro pellets or fine flake foods should form the foundation of their diet. Choose products specifically formulated for small tetras that provide balanced nutrition with appropriate protein levels around 40 to 45 percent. Avoid large pellets that the fish struggle to consume, as uneaten food quickly fouls water quality.

Frozen foods provide excellent supplementation and should be offered several times weekly. Frozen brine shrimp, daphnia, and bloodworms are all eagerly accepted and provide the protein-rich nutrition that enhances coloration. Thaw frozen foods in aquarium water before feeding to prevent temperature shock and digestive issues.

Live foods can be offered occasionally as treats and to stimulate natural hunting behaviors. Baby brine shrimp, microworms, vinegar eels, and small daphnia are all appropriate sizes for these diminutive fish. Live foods are particularly valuable when conditioning fish for breeding or when trying to entice newly introduced fish to eat.

Feed small portions two to three times daily, offering only as much food as the fish can consume within two to three minutes. Costello Tetras have small stomachs and benefit from frequent small meals rather than large infrequent feedings. Observe feeding behavior to ensure all fish are eating, as shy individuals may be outcompeted by bolder tank mates.

Behavior and Temperament

Costello Tetras are among the most peaceful fish available in the aquarium hobby, making them ideal for community tanks with other non-aggressive species. Their tranquil nature extends to interactions with their own kind and other fish, rarely showing aggression even during feeding or breeding activities.

Schooling behavior is a defining characteristic of this species, and they should always be maintained in groups of at least six individuals, though eight to ten or more is preferable. In adequate numbers, they form tight, coordinated schools that move through the water column as a unit. This schooling behavior serves as predator avoidance in the wild and provides security in the aquarium.

When kept in insufficient numbers, Costello Tetras become stressed and may display erratic behavior, hiding, or faded coloration. The security provided by the school allows them to display their full coloration and natural swimming behaviors. Observers often note that fish in larger groups are more active and display more vibrant iridescence.

These fish occupy the middle water column, rarely venturing to the bottom or surface except during feeding. They swim continuously during daylight hours, creating a gentle, soothing movement that adds life to the aquarium. Their swimming style is characterized by quick, darting movements interspersed with brief pauses.

As dither fish, Costello Tetras help encourage shy or newly introduced fish to display more natural behaviors. Their constant, confident movement signals to other fish that conditions are safe, reducing stress and promoting normal activity patterns throughout the community.

Tank Mate Compatibility

Selecting appropriate tank mates for Costello Tetras requires choosing species that share their peaceful nature and environmental preferences. Their small size and tranquil temperament make them vulnerable to aggressive or predatory fish, so careful companion selection is essential.

Other small tetras make excellent tank mates, with Neon Tetras, Cardinal Tetras, Ember Tetras, and Rummy-nose Tetras all sharing similar water parameter preferences and peaceful dispositions. These species often school together, creating a mixed shoal that enhances the visual appeal of the aquarium.

Corydoras catfish, particularly smaller species like Corydoras habrosus or Corydoras pygmaeus, coexist well with Costello Tetras. These bottom-dwellers occupy a different tank region and share the peaceful temperament of the tetras. Avoid larger cory species that might outcompete the tetras for food.

Small rasboras such as Chili Rasboras, Phoenix Rasboras, and Galaxy Rasboras create stunning nano communities when combined with Costello Tetras. All these species appreciate similar soft, acidic conditions and form beautiful mixed schools that display different colors and movement patterns.

Peaceful dwarf cichlids like Apistogramma species or Mikrogeophagus ramirezi can work in larger tanks with plenty of hiding spots, though careful monitoring is required. Dwarf cichlids may become territorial during breeding, so provide ample space and visual barriers if attempting this combination.

Small livebearers including Endler’s Livebearers, small guppy varieties, and smaller platy species can coexist with Costello Tetras. Avoid larger livebearer varieties or aggressive types like swordtails that may harass the smaller tetras.

Shrimp species such as Cherry Shrimp, Amano Shrimp, and smaller dwarf shrimp make excellent tank mates in well-planted tanks. The shrimp help clean algae and detritus while adding interesting behaviors to the lower tank regions.

Absolutely avoid any predatory or aggressive fish. Cichlids like Oscars, Jack Dempseys, or Convicts will eat Costello Tetras. Large tetras like Buenos Aires Tetras may nip fins or outcompete them for food. Betta fish may be too aggressive, particularly in smaller tanks.

Breeding

Breeding Costello Tetras in captivity is achievable for dedicated aquarists willing to provide appropriate conditions and care. These fish are egg scatterers that exhibit minimal parental care, requiring specific setups to maximize fry survival rates.

Sexual dimorphism is subtle but discernible with close observation. Males typically appear slightly more slender and may display more intense coloration, particularly during breeding condition. Females become noticeably rounder when carrying eggs, with a fuller abdomen that contrasts with the streamlined male profile.

Conditioning breeders involves feeding high-quality live and frozen foods for two to three weeks before attempting to spawn. Bloodworms, brine shrimp, and daphnia provide the protein and nutrition needed for gamete production. Maintain water parameters on the softer, more acidic end of their acceptable range during conditioning.

A separate breeding tank of 10 to 15 gallons provides the best chances for successful spawning and fry survival. The tank should contain fine-leaved plants like Java Moss or spawning mops where eggs can fall and be protected from parental predation. Alternatively, a bare-bottom tank with a mesh spawning grate prevents egg predation by keeping adults separated from falling eggs.

Water in the breeding tank should be soft (2-4 dGH), acidic (pH 6.0-6.5), and slightly warmer (78-80°F) than the main tank. Dim lighting helps trigger spawning behavior and reduces stress on the breeding pair. Some aquarists report success using rainwater or reverse osmosis water for breeding setups.

Spawning typically occurs in the morning hours, with the male chasing the female through plants until she releases eggs. The female can lay between 100 and 200 eggs during a single spawning event. Eggs are adhesive and stick to plants, substrate, or tank glass. Remove the adults immediately after spawning to prevent egg predation.

Eggs hatch within 24 to 36 hours depending on temperature, with fry initially carrying yolk sacs that provide nutrition for the first 48 to 72 hours. Once free-swimming, fry require infusoria, paramecium, or commercially available liquid fry food for the first week. Gradually transition to microworms, baby brine shrimp, and finely crushed flake food as they grow.

Fry grow rapidly under good conditions and can reach adult size within six to eight months. Maintain excellent water quality through frequent small water changes, as fry are sensitive to ammonia and nitrite. Separate larger fry from smaller siblings to prevent cannibalism and ensure all receive adequate food.

Health Issues

Costello Tetras are generally hardy fish when provided with appropriate water conditions and nutrition, but they are susceptible to several common freshwater fish diseases. Understanding these health issues enables prompt identification and treatment.

Ich (Ichthyophthirius multifiliis) is the most common parasitic infection affecting Costello Tetras. Symptoms include small white spots resembling salt grains on fins and body, scratching against decorations, and rapid breathing. Treatment involves raising water temperature gradually to 86 degrees Fahrenheit for several days or using copper-based medications in a quarantine tank.

Fin rot, typically caused by bacterial infections like Aeromonas or Pseudomonas, manifests as frayed or deteriorating fins that may progress to body erosion. Poor water quality is usually the underlying cause. Treatment requires improving water conditions and administering antibiotics either in food or water, depending on severity.

Neon Tetra Disease (NTD), caused by the microsporidian parasite Pleistophora hyphessobryconis, affects many tetra species including Costello Tetras. Symptoms include loss of coloration, difficulty swimming, spinal curvature, and eventual death. Unfortunately, there is no cure for NTD, and affected fish should be euthanized to prevent spread.

Gill flukes and skin flukes are parasitic flatworms that attach to fish gills or skin, causing irritation, rapid breathing, and flashing behavior. Treatment requires anti-parasitic medications containing praziquantel or formalin, administered in a quarantine tank to avoid harming beneficial bacteria.

Swim bladder disorder can occur due to overfeeding, constipation, or bacterial infection. Affected fish struggle to maintain buoyancy, floating at the surface or sinking to the bottom. Treatment involves fasting for 24 to 48 hours, then feeding peeled peas or daphnia to relieve constipation.

Frequently Asked Questions

Q: How big do Costello Tetras get? A: Costello Tetras reach between 1.5 and 2 inches in length when fully grown, making them suitable for smaller community tanks.

Q: How many Costello Tetras should I keep together? A: Maintain a minimum of six individuals, though eight to ten or more is preferable for the best schooling behavior and reduced stress.

Q: Can Costello Tetras live with Neon Tetras? A: Yes, these species are fully compatible and often school together, creating beautiful mixed groups with different color patterns.

Q: Do Costello Tetras need soft water? A: While they prefer soft, acidic water (pH 5.5-7.0, soft to moderately soft), they can adapt to moderately hard, neutral conditions if acclimated gradually.

Q: Are Costello Tetras good for beginners? A: Yes, their peaceful nature and reasonable hardiness make them excellent choices for beginners who can provide appropriate water conditions.

Q: What do Costello Tetras eat? A: They accept high-quality flake foods, micro pellets, frozen brine shrimp, daphnia, and bloodworms. Feed varied diet for best health and coloration.

Q: Can I keep Costello Tetras in a 10-gallon tank? A: A 10-gallon tank is the absolute minimum for six individuals, but a 20-gallon or larger tank provides significantly better conditions for their schooling behavior.

Q: Do Costello Tetras jump? A: While not notorious jumpers like some species, they may jump when startled or during spawning. A lid is recommended, especially in smaller tanks.

Q: How long do Costello Tetras live? A: With proper care, Costello Tetras typically live 3 to 5 years, with some individuals reaching 6 years in optimal conditions.

Q: Are Costello Tetras fin nippers? A: No, they are very peaceful and do not nip fins. They are safe to keep with fish that have long, flowing fins.

Q: Can Costello Tetras breed in community tanks? A: While they may spawn in community tanks, eggs and fry are almost always eaten by tank mates or the parents. Separate breeding setups are needed for successful raising of fry.

Q: Do Costello Tetras change color? A: Their iridescent green-gold sheen becomes more pronounced under dim lighting with dark substrate. Stress can cause them to fade, while ideal conditions enhance their metallic appearance.

Q: What fish should I avoid keeping with Costello Tetras? A: Avoid any aggressive or predatory fish including cichlids like Oscars, larger tetras like Buenos Aires Tetras, and predatory catfish.

Q: Do Costello Tetras need plants? A: While not strictly necessary, they thrive in planted tanks that mimic their natural habitat and provide security. Dense planting brings out their best colors and behaviors.

Q: Can Costello Tetras live with shrimp? A: Yes, they are fully compatible with Cherry Shrimp, Amano Shrimp, and other dwarf shrimp species in planted tanks.

Q: How often should I feed Costello Tetras? A: Feed small portions two to three times daily, offering only what they can consume within two to three minutes to prevent overfeeding and water quality issues.

Q: Do Costello Tetras need a heater? A: Yes, they require tropical temperatures between 72-79°F. Use a reliable heater to maintain stable temperatures, especially in cooler climates.

Q: Are Costello Tetras sensitive to water changes? A: They appreciate regular water changes but can be sensitive to large, abrupt changes. Perform weekly changes of 20-30% using temperature-matched, dechlorinated water.

Q: Can Costello Tetras live with Bettas? A: This combination is risky. While some peaceful Bettas may coexist, the Betta’s aggression and the tetra’s small size often lead to problems. Larger tanks with plenty of plants improve chances of success.

Q: What is the difference between Costello Tetras and Neon Tetras? A: Costello Tetras lack the red and blue stripes of Neons, instead displaying an iridescent green-gold sheen with a distinctive black spot near the gills. They are also slightly larger and less colorful but equally peaceful.

Tips for Success

Quarantine all new Costello Tetras for at least two weeks before introducing them to your main tank. This observation period allows you to monitor for disease, ensure they are feeding properly, and acclimate them to your water conditions without risking your established livestock.

Purchase your entire school of Costello Tetras at the same time from the same source whenever possible. This ensures they are already accustomed to each other and reduces the time needed for the group to form a cohesive school. Adding individuals gradually can result in the newcomer being excluded from the group.

Maintain stable water parameters through regular testing and consistent maintenance routines. These fish are sensitive to ammonia and nitrite spikes, so never skip water changes or overfeed. Use a quality liquid test kit rather than strips for accurate readings.

Provide dim lighting conditions to bring out their metallic iridescence. Bright lighting causes them to appear washed out and may increase stress. Use floating plants, dimmable LED fixtures, or place the tank away from direct sunlight to achieve appropriate lighting levels.

Use dark substrate and background to enhance the visibility of their coloration. Light-colored gravel and backgrounds make their subtle colors difficult to see, while dark colors create contrast that highlights their green-gold sheen.

Feed a varied diet that includes both prepared and frozen foods. Relying solely on flake food leads to nutritional deficiencies and faded colors. Rotate between high-quality flakes, frozen bloodworms, brine shrimp, and occasional live foods for optimal health.

Include botanicals like Indian Almond Leaves or driftwood in their tank. These natural elements soften water, create tannins that tint the water tea-colored, and provide foraging opportunities. The tinted water also reduces light intensity and makes the fish feel more secure.

Observe your school daily for changes in behavior or appearance. Healthy Costello Tetras should swim actively in the middle water column with tight schooling behavior. Any fish separating from the group, hiding excessively, or showing faded colors may be experiencing stress or illness.

Avoid sudden changes in water parameters or tank conditions. When performing water changes, ensure new water matches the tank temperature and pH as closely as possible. Gradual acclimation to new conditions prevents stress and shock.

Finally, appreciate these fish for their subtle beauty and peaceful nature. While they may not have the flashiest colors in the aquarium hobby, their iridescent shimmer and graceful schooling behavior create a tranquil, natural atmosphere that more flamboyant species cannot match. With proper care and attention to their environmental needs, Costello Tetras will reward you with years of serene beauty.