Treasures in the Dark- The Blind Cave Tetra (Astyanax mexicanus)
Amongst the numerous species of freshwater aquafauna, the Blind Cave Tetra (Astyanax mexicanus) captivates the interest of many aquarists, not only because of its rather eerie appearance but also due to its evolutionary adaptations to life in darker habitat conditions. These “eyeless creations of nature” will be a unique addition to your aquarium intensifying its tropical resemblance.
What’s Unique About Blind Cave Tetra?
The Blind Cave Tetra, commonly known as the Mexican Tetra, is a member of the family of fish, Characidae and is regarded as native to the caves of northeastern Mexico. These subterranean environments are relatively pitch-dark. The deficiency of a light has made vision rather impossible signifying the irrelevance of an eyesight. Even though these fish species are completely blind, their loss of eyes is compensated by the high development of other senses including a heightened lateral line system that detects vibrations and fluctuations in the surrounding habitat. Despite evolutionarily losing their eyes, these blind cave tetras have adapted light-responsive cells on their body and display an endogenous circadian rhythm, which means their physical, chemical, and behavioral changes correlate with the 24-hour cycle.
Scientific Classification and Basic Morphology
As per the binomial nomenclature, Blind Cave Tetra is named Astyanax mexicanus, with the genus name which depicts its linkage to Mexico.
- Scientific Name- Astyanax mexicanus
- Family- Characidae
- Order- Characiformes
- Common Name(s)- Blind Cave Tetra, Mexican Blind Cavefish
- IUCN Conservation Status- Least Concern (LC)
Another significance is that there are 2 forms of A. mexicanus belonging to the same species: cave-dwelling form and surface-dwelling form. While the cave-dwelling form of Astyanax mexicanus is blind and lacks pigmentation, the surface-dwelling variety retains eyes and coloration. One of the most prominent differences is the absence of eyes, known as the regressive trait because the surface fish that originally colonized caves possessed eyes. In the aquarium trade, the cave form is typically seen.
Blind Cave Tetras generally grow to about 3 - 5 inches (total length), with a streamlined, torpedo-shaped body. Their coloration ranges from silvery-white to a pinkish tone. Since they lack pigmentation, their pale skin often gives them a translucent appearance. Their vestigial eyes are barely visible, they are covered by a thin layer of skin. This makes Blind Cave Tetras one of the most distinct fish found in aquariums.
Distribution and Habitat of Blind Cave Tetras
Blind Cave Tetras are native to the Nearctic realm, basically found in cave systems of northeastern Mexico, particularly the Sierra de El Abra caves. These subterranean rivers are entirely devoid of light, which led to the fish fully devolving the use of its eyes and the need for pigmentation. Their surface-dwelling variety, however, can be found in rivers and streams across Mexico and parts of the southern United States. They are found in the mid level above the rocky and sandy bottoms of water pools, and backwaters of creeks and streams in their habitat. These fish prefer waters with a pH ranging from 6.5-8 and an approximate temperature range of 20-25 °C. In winter, there are records of some populations migrating into warmer regions.
Behavior and Special Characteristics
Blind Cave Tetras do not consider their lack of eyes as a disadvantage. Despite this, they are very active fish that use their lateral line system to facilitate undisrupted locomotion and navigation. They can detect the slightest changes in water pressure and vibrations, allowing them to swim confidently around obstacles and locate food avoiding potential threats. These fish are also social and display schooling behavior with other tetras. One of the other key behavioral characteristics is that they can go for an extended period without food, a trait inherited from their cave-dwelling ancestors.
Breeding of Blind Cave Tetras
It is rather an interesting and straightforward activity to breed Blind Cave Tetras. These fish are egg-layers and free-spawners, meaning the female will scatter eggs, usually near plants or rock surfaces.
An overview of the breeding procedure
- Set up a tank suitable for breeding that can hold up to at least 35-38 litres of water
- Install a gentle filtration system to avoid any disturbance to the eggs
- The breeding pair should be perfectly conditioned by feeding them high-quality food (Ex. live or frozen brine shrimp or bloodworms)
- Carefully monitor the water parameters such as the temperature and pH levels, and always try to maintain a temperature between 20-23°C (70°F to 75°F).
- Once the eggs are laid and then fertilized, remove the pair from the tank to prevent them from feeding on the eggs
- The eggs will hatch in about 24 to 48 hours, and the fry becomes free-swimming after 4 days
It should be noted that the fry may initially have eyes, but later on, they will disappear.
Blind Cave Tetra in Ornamental Fish-Keeping
Blind Cave Tetras are popular among ornamental fish due to their unique morphology and hard nature. These fish are social and do not display any aggressive behavior which makes them compatible tank mates for a variety of other species and thrive in community tanks. Because they rely on their lateral line system to move around, they do not need light and prefer dimly lit tank aquariums.
They can coexist with other non-aggressive species. Ideal tank mates include; Neon tetras, cardinal tetras, and Corydoras catfish, which share the bottom-dwelling behavior, as well as danios and rasbora species.
Ideal Tank Conditions for Blind Cave Tetras
Tank Size
Even though Blind Cave Tetras are relatively small fish, they are active swimmers. A minimum tank size of 75 litres is recommended for a small group of 5-6 fish. For larger schools or community setups, a tank size of 110-115 litres or more is preferable.
Water Conditions
Adequate water conditions are crucial in maintaining perfect care for these tetras
- Temperature- about 20°C to 25°C, slight fluctuations can be tolerated
- pH- neutral to slightly alkaline water, with a pH of 6.5 to 8.0.
- Hardness- a moderate level of water hardness of 5-19 dGH is ideal.
Tank Setup and Aquascaping
To mimic the cave environments that Blind Cave Tetras are accustomed to, you should provide them with a tank with high availability of hiding places. Darker substrates, such as black gravel or sand, contrast beautifully with their pale bodies. Rocks, caves, and driftwood will provide a natural habitat for them to explore and rest.
Since these fish evolved in complete darkness, lighting should be subdued. You can also add floating plants to diffuse the light and create shaded areas. You can visit Melbourne Tropical Fish for guidance about the Blind Cave Tetra tank setup and scaping. The necessary tank components are also available in-store for purchase.
Filtration and Tank Maintenance
A good filtration system is essential for maintaining clean water, as Blind Cave Tetras are sensitive to the water quality. A gentle filtration system is ideal as much stronger filters can disturb their natural behavior causing them to stress out.
Regular water changes are needed. Approximately a 20-30% water change every two weeks to ensure optimal water quality is ideal.
Diet and Feeding of Blind Cave Tetras
Their natural diet comprises aquatic invertebrates such as crustaceans, annelids, arthropods, their larvae, insects such as water beetles, algae, and other aquatic vegetation. In aquariums, they are omnivorous and will consume high-quality flake food, pellets, and frozen foods like bloodworms or brine shrimp. You can visit Melbourne Tropical Fish to purchase the required fish food, it is available in a wide range of varieties and at affordable prices.
LifeSpan of Blind Cave Tetras
In aquariums under proper care, they can live up to a maximum of 10 years. This comparatively long lifespan makes them a good addition to any aquarium.
Where to Buy Blind Cave Tetras
If you are looking for a trusted place to buy Blind Cave Tetras, Melbourne Tropical Fish is the best place. Melbourne Tropical Fish offers a wide selection of ornamental fish, including Blind Cave Tetras, ensuring customers receive healthy, well-cared-for fish. With expert advice and a commitment to quality, Melbourne Tropical Fish is your go-to source for all your aquarium needs.
Adding the Blind Cave Tetra to Your Aquarium
Blind Cave Tetras are more than just an eerie fish species, they are evident species concerning evolution and adaptability. Therefore, you can be a seasoned aquarist or even a beginner looking to expand your fish collection, Blind Cave Tetras will be a great addition to it. For the best selection and expert advice, head to Melbourne Tropical Fish, where you can purchase these fascinating fish and all the supplies you need to create the perfect tank setup and conditions for them.