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How to Identify Tetras

Adding tetras is an easy way to bring bright colors to your community aquarium. Also known as characins due to their placement in family Characidae, tetras can range in length from half an inch to 3 feet.Tetras are active in the aquarium and will swim in schools with their own kind, while coexisting harmoniously with other fish and plants.

Tetra Characteristics

Tetras have long, slender fins with an extra fin known as the adipose fin, situated between the dorsal and caudal fins. The forked tail fin gives the tetra the ability to swim fast. In combination with its fusiform streamlined body, it's able to maintain an energetic level of nearly constant activity in an aquarium. Brilliant colors and patterns along their sides not only make them shine brightly in an aquarium, but provide disruptive patterns that can help them hide from predators.

Identifying Similar Species

Some species of tetra are easily confused with each other. Neon tetras, commonly sold in fish stores, are often confused with glowlight and cardinal tetras. Cardinals and neons have a blue stripe that runs from nose to tail, while glowlights have a yellow-green stripe. All three species have red tail markings accompanying the stripe; neons' and glowlights' stripes run from belly to tail, while cardinals have red coloration over the majority of their lower bodies.

Identifying Sex

Identifying the sex of a juvenile tetra is nearly impossible, but adult fish can usually be differentiated even though many species' males and females have identical coloration. Physical differences occur in shape and size. Females are usually larger than males and have a wider belly to accommodate eggs. They also have smaller dorsal and anal fins without ray extensions, while male fins are longer with bony ray extensions.

Identification through Vents

The sex of a larger tetra can be determined by turning it on its back and examining the vents between the pectoral and anal fins. The smallest opening closest to the head is the anus, and between it and the tail is the vent. A female tetra will generally have a larger vent for passing eggs. The male releases milt to fertilize eggs from his vent, which is usually smaller and more slit-like.