The Ruby Tetra, scientifically known as Axelrodia riesei, is a diminutive and strikingly colored freshwater fish native to the clear waters of South America, particularly in Colombia. This small tetra is highly valued in the aquarium trade for its vibrant coloration and peaceful demeanor, making it a favorite among enthusiasts who appreciate both beauty and tranquility in their aquatic setups.

Ruby Tetras are characterized by their vibrant ruby-red bodies, which can range from a bright pinkish hue to a deeper red, depending on the lighting and water conditions. They typically have a compact, streamlined body shape common among tetras, with relatively large eyes that enhance their delicate appearance. The fins of the Ruby Tetra are usually clear or slightly tinted, which accentuates their vivid body color.

In captivity, Ruby Tetras thrive in soft, slightly acidic water conditions that replicate their natural habitat. They are best housed in well-planted aquariums that offer plenty of hiding spots and a subdued lighting setup to mimic the shadowed areas of their native streams. The presence of dark substrate and background can also help in enhancing their brilliant coloration.

Being a schooling fish, Ruby Tetras should be kept in groups of at least six or more to ensure their well-being and promote natural behavior. In a school, these tetras are more active, confident, and visually impressive, displaying their schooling behaviors and interactive dynamics, which add to the overall vibrancy of the tank.

Their diet should be varied and rich in quality nutrients. Small-sized flake foods, micro pellets, and a regular offering of small live or frozen foods such as daphnia or brine shrimp will help maintain their health and coloration. A balanced diet is crucial to keep them vibrant and active.

Breeding Ruby Tetras can be a challenging yet rewarding experience. They typically scatter their eggs among fine-leaved plants in soft, acidic water. To increase breeding success, it's advisable to condition the breeding pair with high-quality foods and maintain optimal water conditions. After spawning, it is recommended to remove the adults to prevent them from consuming the eggs or fry.

Overall, the Ruby Tetra is an excellent choice for both novice and experienced aquarists looking for a peaceful, beautiful, and relatively easy-to-care-for species. Their small size and minimal care requirements make them ideal for community tanks, where their stunning color and gentle nature can be appreciated amidst a diverse group of similarly tempered fish.