Glass Tetra

Adult glass tetras reach about 6 cm in length. Their body is almost completely transparent, allowing you to see the spine and internal organs clearly. The only coloured part is the red tail. Sexual dimorphism is slight, but males can be distinguished by a slightly elongated, pointed edge of the anal fin that resembles a spine.

This species is widely distributed throughout the Amazon, occurring in Ecuador, Colombia, Peru, Bolivia and Brazil. These fish prefer to stay in the upper water column, living in shallow streams, small rivers and channels connecting larger bodies of water; they are rare in the main channels of large rivers.

Glass tetra is a peaceful, very active schooling species that should be kept in groups of 6–8 individuals. With fewer fish, skirmishes between males over dominance are possible. Thanks to its excellent adaptability to different water conditions, the glass tetra gets along well with many other fish of similar size and temperament. However, it should not be kept with surface-dwelling fish such as hatchetfish, to avoid unnecessary competition for food and territory.

To keep 6–8 of these fish you will need a tank of at least 70 litres. It is best to include plenty of plants, arranged so that enough open space remains for swimming. Floating plants are also welcome, providing refuge during stress. The bottom of the tank has no special requirements and can be decorated as you like—for example, with sandy substrate and decorative elements such as driftwood, sunken ships or castles. Water pH and dGH can be in fairly wide ranges, making this species tolerant of change. To mimic natural conditions, you can add some dried leaves of deciduous trees and/or cones, along with oak bark, to the bottom. As tannins dissolve over time, they will give the water a slight brownish tint. Leaves should be dried in advance, soaked until they sink, and only then placed in the tank. Replace leaves every two weeks and cones once a month. A similar effect with less effort can be achieved using a cloth bag filled with alder cones, or a filter with alder cone media. Aquarium peat should be bought only from specialist pet shops, as it is specially treated.

The glass tetra feeds at the water surface, so it must be offered only floating foods. In the home aquarium it readily accepts all types of dry, frozen and live foods. Remember that food quality directly affects the overall health and colour of your fish, so use only foods from trusted, well-known manufacturers.

The glass tetra is an egg-scatterer, but it has weak parental instincts, so eggs and fry may be eaten by adults. For successful breeding, prepare a separate spawning tank. A 20-litre tank is usually suitable; its decor is not critical. To protect future fry, line the bottom with fine-mesh netting, 1–2 cm glass beads or dense thickets of low, fine-leaved plants and mosses. Before adding the fish, fill the tank with water from the main tank. Lighting should be dimmed, and a standard sponge air-lift filter and heater are sufficient. Spawning is triggered by establishing water parameters: pH 6.0–6.5, dGH 1–5, at 25–26 °C. The diet of breeding fish should include a large proportion of protein foods such as bloodworm, daphnia and brine shrimp. After some time the females will noticeably round as they fill with eggs. Then remove the females and the largest, brightest males to the spawning tank. Once spawning is complete, return the parents to the main tank. Fry hatch from the eggs in 14–36 hours and begin active swimming on day 3–4, after which they need specialized fry food.

The best guarantee of fish health against disease is a balanced aquarium ecosystem with optimal keeping conditions. If you notice changes in behaviour or colour, unusual patches or other symptoms, check the water parameters first, and only then proceed with treatment.

When choosing a glass tetra, check the clarity of its body: in a healthy fish it should be clean, without cloudy patches, ulcers or visible parasites. Fish should swim actively in the water column and stay in a school, as solitary or lethargic behaviour often indicates stress or disease. Avoid fish with damaged fins or signs of emaciation shown by a distinctly concave belly.