Minimum Tank Size: 29 Gallons (110 Liters)
Care Level: Moderately Hard
Water Conditions: PH 6.5-8.0 and Moderately Hard to Very Hard
Temperature: 68-77 °F (20-25 °C)
Maximum Size: 4.7 inches (12 centimeters)
The blind cave tetra (Astyanax mexicanus) is a truly unique fish, and its strange appearance makes it a perfect centerpiece for most aquariums. While there are numerous species of sightless fish, these are the only ones regularly available for sale.
The blind cave tetra is actually an eyeless, albino variant of the unremarkable Mexican tetra, which is native to Southern Texas, as well as central and eastern Mexico. The blind variant only originates from several distinct cave populations in Mexico, and the level of sightlessness varies significantly between the different populations. Some of the fish only have reduced eyesight, while others have lost their eyes completely.
But far from bumping helplessly around their aquariums, these fish are actually accomplished navigators. They can navigate by using their lateral lines and are able to detect fluctuations in water pressure. If they weren’t missing their eyes, it would be difficult for a casual observer to notice these fish were blind simply by watching their behavior in an aquarium.
Blind cave tetras stay relatively small in the home aquarium, and they grow to a maximum of 4.7 inches (12 cm). The natural form of Mexican tetras have a drab, silver coloration, while the albino cave variant has a notable pinkish color.
Blind cave tetras are a peaceful fish, although they have been known to become more aggressive as they age. While the blind variant doesn’t seem to be a schooling fish, they do still tend to congregate in the water, and do best when kept in groups of at least six. Because of their size and the recommendation to keep them in a group, they should be provided with at least a 29 gallon (110 liter) tank.
They may occasionally nip their tank mates, and this is especially true during feedings. This is the result of their blindness, as they search for food with their mouths. However, unlike other fin nipping fish, this rarely becomes a problem unless they are kept with very docile, slow moving fish.
These fish live in a rocky environment in their natural habitat and this should be recreated as closely as possible in their aquarium. Because they are blind, they can be kept in very basic setups, and adding live plants or decorations is purely at the discretion of the aquarist. Their tank should be dimly lit, and natural light should also be kept to a minimum.
When a new object is added to their aquarium, these fish will increase their swim speed, which is believed to stimulate their lateral lines. They will then memorize the location of the new object, and add it to their mental map of the aquarium.
A high quality filter is a must for these fish, and usually the best choice is a hang on back filter. One of the best filters on the market is the Aquaclear Power Filter. This filter combines excellent filtration with a durable design, and it will keep a fish tank sparkling clean.
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The blind cave tetra primarily feeds on insects, crustaceans and worms in the wild, though they will accept a wide range of prepared foods in the home aquarium. Their diet should consist of a high quality flake food, and I personally recommend New Life Spectrum pellets. It helps to enhance the color of fish, and only contains premium ingredients.
Their diet should also be supplemented with regular feedings of live or frozen food. Frozen bloodworms, blackworms, brine shrimp, and daphnia are all greedily accepted by these fish.
While an aquarist may be concerned that a blind cave tetra will have difficulty finding food, it has significant differences from the regular Mexican tetra, which allows it to easily locate food. It has a much stronger olfactory sense, and has taste buds spread across its head. Therefore, it is quite capable of finding food in an aquarium even without vision.
Blind cave tetras can cross breed with Mexican tetras, so it’s recommended not to keep these species of fish together in the same tank. The females can usually be identified by their larger, more rounded bodies and their straight anal fin. The males on the other hand have a slightly curved anal fin, and their bodies are generally narrower than the females.
These fish are quite easy to breed, though a breeding tank will usually be required. The breeding tank should have a substrate of marbles, or any other material that will prevent the adults from reaching the eggs. The tank should also have a sponge filter, which is the safest filter for fry (hang on back filters are notorious for killing fry).
Male and females should be identified and moved to separate tanks prior to breeding. There they should be conditioned for at least a week by feeding them high quality live and frozen foods. At the end of the week, the healthiest looking male and female should be selected.
The chosen male and female should then be introduced to the breeding tank and under normal circumstances will spawn by the next morning. If no eggs are visible by the following morning, the original pair should be removed, and replaced with another pair. This should be repeated until eggs have been laid.
Blind cave tetras can lay up to 1000 eggs per female and the freshly laid eggs appear white. Many people associate white eggs with being infertile, but it’s quite normal for blind cave tetras. The eggs will hatch in around 24 hours, and the fry will usually become free swimming within a week.
When the fry become free swimming they should be feed infusoria. After about a week, they can then be moved onto baby brine shrimp, microworms, or any of the commercially available fry foods. Usually within the first month they can be introduced to powdered prepared foods.
You may notice that the fry are born with what appear to be functioning eyes, though they will eventually become covered in a layer of skin, and disappear inside of the fish.