Astyanax mexicanus (Blind Cave Tetra)

Overview

The Blind Cave Tetra, scientifically known as Astyanax mexicanus (often referred to as Astyanax jordani in its blind form), is one of the most remarkable species available in the aquarium hobby. Having evolved in complete darkness, these fish have completely lost their eyes and pigmentation. Instead, they navigate their environment and locate food using a highly sensitive lateral line system. They are incredibly hardy and active, making them a great choice for both beginners and experienced aquarists looking for something unusual.

Distribution and Habitat

This unique species originates from a series of limestone caves in the central and eastern regions of Mexico. In their natural habitat, they live in subterranean pools and streams where there is absolutely no light. The water in these caves is typically hard and alkaline. Interestingly, there are surface-dwelling populations of the same species that possess normal eyes and pigmentation, but the blind cave variant is the one predominantly kept in the hobby.

Description of Blind Cave Tetra

Body shape:

They possess a classic, somewhat deep and laterally compressed tetra body shape, similar to their surface-dwelling relatives. They are robust and built for active swimming.

Color:

Due to the lack of melanin and other pigments, their bodies are a translucent pale pink to silvery-white color. The pinkish hue is actually the result of their blood vessels showing through their unpigmented skin.

Barbels:

They do not possess barbels.

Snout:

The snout is slightly rounded, typical of many characins, with a mouth oriented to feed from the middle and bottom of the water column.

Eyes:

As their name suggests, adult Blind Cave Tetras have no functional eyes. While fry are born with rudimentary eyes, these are quickly reabsorbed and covered by skin as the fish matures.

Fins:

The fins are completely transparent and lack any coloration or distinct markings.

The Tail:

They feature a deeply forked caudal fin, which aids in their swift and continuous swimming behavior.

Temper

Blind Cave Tetras are generally peaceful, though they are very active and sometimes boisterous. Because they navigate by sensing water movement, they may occasionally bump into other fish. They are best kept with other robust, active species, as their frantic swimming and feeding habits might stress out shy or slow-moving tank mates.

Sociality

They are a highly social schooling fish. To keep them comfortable and reduce any potential stress, they should be kept in groups of at least 6 to 8 individuals. In a group, they will establish a pecking order and display their natural schooling behaviors.

Activity

These tetras are in constant motion. They spend their days actively patrolling the middle and lower levels of the aquarium, continuously exploring their surroundings and searching for food using their lateral line and sense of smell.

Keeping and Caring for Blind Cave Tetra

Tank size:

A minimum tank size of 20 to 30 gallons is recommended. Because they are so active and can grow up to 4 inches (10 cm), they need plenty of horizontal swimming space.

Water Parameters:

Temperature

They prefer cooler to moderate tropical temperatures, ideally between 20-25°C (68-77°F).

pH

They thrive in neutral to slightly alkaline water, with a pH range of 6.5 to 8.0.

Hardness

Reflecting their limestone cave origins, they prefer moderately hard to hard water, roughly 8 to 20 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept below 20 ppm through regular water changes and tank maintenance.

Lighting

While they come from pitch-black environments, they adapt perfectly well to standard aquarium lighting. However, they will be most comfortable in a tank with dim lighting or floating plants to diffuse the light.

Water flow

A moderate water flow is appreciated, simulating the subtle currents found in their native subterranean streams.

Decorations and Plants

The tank should be decorated with smooth rocks, caves, and driftwood. Since they are blind, avoid sharp or jagged decorations that could cause injury when they bump into them. Plants can be included, but ensure there is ample open swimming space.

Diet

Blind Cave Tetras are omnivorous and not picky eaters. In the aquarium, they will readily accept high-quality flakes, micro-pellets, and a variety of live or frozen foods such as bloodworms, daphnia, and brine shrimp.

Some Feeding Tips

Despite being blind, they have an incredibly acute sense of smell and will often be the first to find food when it hits the water. Ensure that food reaches the middle and bottom of the tank, and watch that they do not outcompete slower, sighted fish during feeding time.

Breeding

Breeding the Blind Cave Tetra is relatively easy. They are egg scatterers and exhibit no parental care. To breed them, set up a separate breeding tank with dim lighting, a sponge filter, and a mesh or marbles on the bottom to protect the eggs from being eaten. Condition the breeders with high-quality live foods. After spawning, remove the parents. The eggs will hatch in a few days, and the fry can be fed infusoria until they are large enough for baby brine shrimp.

Conclusion

The Blind Cave Tetra is an extraordinary example of evolutionary adaptation. Their lack of eyes and pigment, combined with their hardiness and energetic nature, make them a captivating addition to a community aquarium. If provided with adequate swimming space and appropriate tank mates, these unique fish will thrive and provide endless fascination for any aquarist.