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Blind Cave Tetra Fact Sheet
The "Blind Cave Tetra", "Astyanax fasciatus mexicanus", is a very unusual fish. It is completely devoid of skin pigments and
has a pink skin due to the haemoglobin in its blood. The most
distinctive part is that it has no eyes as an adult. For the first two weeks of life it does have eyes and certainly appears 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 "Silvery Tetra".
It grows to about three and a half inches long (9cm). The life span is about 5 years.
The
Blind Cave Tetras can find their way around an aquarium without much
trouble. It is not completely clear how they do this. They have a goodsense of smell which helps them locate food, but this does not fully
explain how they navigate around 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 hesitated about even
using it in a descriptive article about fish. If you prefer other
explanations for the formation of this sub species, I am quite happy
with that.
What appears to have happened is that some fish of the species Astyanax fasciatus
found their way into an underground cave system in Mexico. These fish
had eyes and could see as most fish can. In the darkness their eyes were of little use, and eyes use up energy as well as a substantial
amount of brain power to interpret images. The fish that did not use so
much energy and brain power for their eyes had an advantage and bred
more. Over many generations the fish without eyes replaced the fish
with eyes and the new sub species was formed.
I should explain
that the phase "Sub species" does not suggest any form of inferiority,
but is simply a taxonomic group below the level of species, but above
that of variety.
The Blind Cave tetra is not considered a
separate species from the fish that stayed on the surface and kept
their eyes. (In light, vision is an advantage.) The blind cave tetra
will still breed freely with their 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 sighted cousin is found a little further south in Central and
northern South America.
Water Conditions
The
Blind Cave Tetra is a very tough fish, so although its ideal
temperature range may be between 20 and 30 degrees C (68 to 86 degrees
F), they will survive water a little bit hotter than this as well as
much colder, so they are suitable for either a tropical or an unheated
tank.
They can take some acidity (down to about 6) or some
alkalinity (up to about 8), so as long as you avoid extremes this
should not be a problem.
Blind Cave Tetras can take quite high levels of hardness in the water.
Food
The
Blind Cave tetra is a very easily fed omnivore. They will eat all
normal types of fish food and have the ability to eat much faster than
most fish, and a lot at one time. It is a good idea to give them a
variety of foods.
Companions
Some sources describe
the Blind Cave Tetra as being 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.
Fish more suited to be companions for Blind Cave Tetras are: Red
Eye Tetras and other tetras, barbs, Danios of similar aggression. as well as the Corydoras catfish like the Peppered
Catfish.
Some people keep Blind Cave Tetras in an unheated aquarium with Goldfish, Rosy Barbs
and other suitable fish. This can work all right, but I would
definitely avoid the fancy goldfish with long fins or big eyes. With
comets or shubunkins a bit bigger than the Blind Cave Tetras in the
tank they should be fine, but always keep an eye on your fish, and
avoid huge size differences between the different fish.
Do not put the Blind Cave Tetra with large or predatory fish like the larger cichlids or Great White Sharks.
Sexing
The females become much plumper than the males when they are loaded with eggs.
Breeding
The
Blind Cave Tetra is an egg scatterer. They are easy to condition for
breeding because they eat so readily and so much at each meal. They are
stimulated to breed by a drop in temperature. 18 - 20 degrees C (64-68
degrees F) seems a suitable spawning temperature. The parents should be
removed after spawning, but the eggs should not be disturbed.
The
females only lay about 100 eggs each, which is less than the great
majority of tetras. The eggs are also much larger than with most tetras
and should hatch in between 1 and 3 days, and the fry should be free swimming in 6-7 days from spawning.
Because
of their large size, the babies will eat larger things earlier than
small fish. The babies can see for about two weeks. They will eat
protozoa (infusoria) like most baby fish, but can also eat things like
the finest screened daphnia. Commercial fry foods are also suitable.
The babies are vigorous and should grow well.
Pest Fish
Ensure your pet
fish cannot get out into ecosystems they are not native to. The
potential for ecological damage by the Blind Cave Tetra is considerable.
Sources
This fact sheet also appears on the international version of our website at bettatrading.com
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