Blind Cave Tetra Datasheet
The “Blind Cave Tetra”, “Astyanax fasciatus mexicanus”, is a very unusual fish. It is completely devoid of skin pigments and has pink skin due to the hemoglobin in its blood. The most distinctive part is that it does not have adult eyes. During the first two weeks of life it has eyes and it certainly seems to be able to see.
There are several other common names for the Blind Cave Tetra, these include: the “Blind Cave Fish”, the “Mexican Tetra” and the “Silver Tetra”.
It grows to about three and a half inches long (9 cm). The shelf life is about 5 years.
Blind Cave Tetras can orient themselves in an aquarium without much trouble. It is not entirely clear how they do it. They have a good sense of smell that helps them locate food, but this does not fully explain how they move through an aquarium. There are several theories and they are being studied.
A recent example of evolution?
For some people, “Evolution” is a dirty word, so I was hesitant to even use it in a descriptive article on fish. If you prefer other explanations for the formation of this subspecies, I am quite happy with that.
What appears to have happened is that some fish of the Astyanax fasciatus species found their way into an underground cave system in Mexico. These fish had eyes and could see like most fish can. In the dark, their eyes were of little use, and the eyes expend both energy and a substantial amount of brain power to interpret images. Fish that didn’t use as much energy and brain power for their eyes had an advantage and reproduced more. For many generations, eyeless fish replaced eye fish and the new subspecies was formed.
I must explain that the “Subspecies” phase does not suggest any form of inferiority, but is simply a taxonomic group below the species level, but above the variety level.
The blind cave tetra is not considered a separate species from the fish that stayed on the surface and kept their eyes. (In the light, vision is an advantage). The blind cave tetra will still breed freely with its sighted cousins, so this is not an example of the formation of a new species.
Distribution
The blind cave Tetra is found in caves in Mexico and Texas, while its seer cousin is found a little further south in central and northern South America.
Water conditions
The Blind Cave Tetra is a very hardy fish, so although their ideal temperature range may be between 20 and 30 degrees C (68 to 86 degrees F), they will survive water a little warmer than this and much colder, so they are suitable for a tropical or unheated tank.
They can take some acidity (up to about 6) or some alkalinity (up to about 8), so as long as you avoid extremes this shouldn’t be a problem.
Blind Cave Tetras can have quite high levels of hardness in water.
Meal
The blind cave tetra is an omnivore that feeds very easily. They will eat all normal types of fish food and have the ability to eat much faster than most fish, and a lot at a time. It is a good idea to give them a variety of foods.
Companions
Some sources describe the Blind Cave Tetra as peaceful. This is not my experience. I would definitely avoid putting them with small fish like Neon Tetras and Cardinal Tetras, as well as slow-moving long-finned fish like Siamese Fighting Fish, Guppies, and Endlers Guppies.
The most suitable fish to be companions to the Blind Cave Tetras are: Red Eyed Tetras, Silver Tip Tetras, Gold Barbs, Cherry Barbs, Pristella Tetras, Rummy Nose Tetras, Harlequin Rasboras, Scissor Tail, Lemon Tetras, Emperor Tetras, Head and Tail Light Tetras, Bloodfin Glass Tetras, Swordtails, Platies, Mollies, Zebra Danios, Glowlight Tetras, White Cloud Mountain Minnows, Black Widow Tetras, Rosy Barbs, Tiger Barbs , Paraguay Tetras, Penguin Tetras, Buenos Aires Tetras and Colombian Tetras, as well as Corydoras catfish such as pepper catfish.
Some people keep Blind Cave Tetras in an unheated aquarium with Goldfish, Rosy Barbs, and other suitable fish. This can work well, but you would definitely avoid fancy goldfish with long fins or big eyes. With kites or shubunkins slightly larger than Blind Cave Tetras in the tank, they should be fine, but always keep an eye on your fish and avoid large differences in size between different fish.
Do not place the Blind Cave Tetra with large fish or predators such as larger cichlids or great white sharks.
Sexed
Females become much fatter than males when loaded with eggs.
Breeding
The Blind Cave Tetra is an egg spreader. They are easy to condition for breeding because they eat a lot and a lot at every meal. They are stimulated to reproduce by a drop in temperature. 18-20 degrees C (64-68 degrees F) seems like a suitable spawning temperature. The parents should be removed after spawning, but the eggs should not be disturbed.
Females only lay around 100 eggs each, which is fewer than the vast majority of tetras. The eggs are also much larger than with most tetras and should hatch between 1 and 3 days, and the fry should swim freely within 6-7 days of spawning.
Due to their large size, babies eat bigger things earlier than small fish. Babies can see for about two weeks. They feed on protozoa (infusoria) like most baby fish, but they can also eat things like the finest screened daphnia. Commercial fried foods are also suitable. Babies are vigorous and should grow well.
Plague fish
Make sure your pet fish can’t get out into non-native ecosystems. The potential for ecological damage from the Tetra blind cave is considerable.