Blind as a Cave Fish
By Dr David Ford, Consultant to Aquarian®, member of Halifax AS
In the depths of the ocean there are fish with huge eyes
to capture what light penetrates the fathoms. Fish that live in caves receive
no light at all, so even big eyes are of no use. Fish that migrate from open waters
to deep caves gradually lose the use of eyes and other senses take over. This
requires genetic modifications that occur over millions of years and trillions
There are many such species but few of them reach the hobby.
Examples of those that do include Caecobarbus geertsi , the Blind Barb from caves
in the Congo, Clarias cavernicola, the Blind Cave Walking Fish from caves in Namibia
and Ambylopsis platyrhinus, the Kentucky Blind Fish. Unavailable for political
reasons are the Cuban Blind Fishes, Lucifuga and Stygicola species.
these fish are not actually eyeless. Normal fish migrated from surface waters
into deep caves and the eye functions deteriorated over generations. They were
replaced by sensory papillae that sense water movement, taste and smells to give
the fishes' brains a picture of their world despite the complete blackness we
An aquarium fish
dealer in the USA, back in 1936, heard rumours of blind fish in Mexico and commissioned
local Indians to collect any fish from caves at San Luis Potosi. The Indians waded
through many narrow caves, often blocked by fallen rocks. They found skeletons
of dead animals swept into the caves by waters from the Rio Tampaon and fear of
death must have kept earlier collectors from exploring deeper.
for a kilometre the men discovered a huge cave 'big enough to hold a cathedral'
filled with magnificent stalagmites and stalactites and deep water containing
the first collected specimens of the Mexican Blind Cave Fish. That dealer was
C. Basil Jordan of Dallas, Texas and he received 75 specimens of the 100 fish
collected by the San Luis Potosi expedition. All survived and he successfully
bred the fish in aquaria, introducing a new species to the hobby that continues
to this day with mass production in Singapore fish farms.
in a Name
The fish Jordan discovered was declared a new species and
placed in the genus Anoptichthys (named by Hubbs & Innes 1938) with the species
name jordani after the Dallas dealer. Its common name in the USA became the Blind
Cave Tetra and when specimens were imported into Germany the fish was called Blinder
Hohlensalmer (Blind Cave Tetra). The French opted not to name the fish, only listing
the Latin name, but the Poles called it the Blind Cave Fish (Slepiec Jaskiniowy),
which was also adopted by the UK. The Spaniards call it the 'Fish Blind of the
Caves', Pez ciego de la cueves.
However, as the years passed it was noted
that the Southern USA and much of Central America had more than 75 species of
a Characin called Astyanax (named by Baird & Girard 1854) many of which resembled
Anoptichthys jordani in all but colour. The Blind Cave Tetra became the Blind
Cave Characin in American literature.
Several scientists renamed the fish
(e.g. A. hubbsi and A. antrobius) before ichthyologist Sadoglu proved the fish
to be a cave-dwelling form of the Astyanax fasciatus and so it was renamed Astyanax
fasciatus mexicanus. Even today any of the above names can be seen in encyclopedia
of fishkeeping, but the UK aquarium trade know the fish as The Blind Cave Fish.
What better fish to use for
feeding trials? Being blind it must choose edible items on taste alone. Hence,
when developing Aquarian® in the Aqualab back in the 1970s, specimens of Blind
Cave Fish were installed for testing various recipes.
The fish was fascinating
- it swam with a waggle that obviously alternated left and right lateral lines
to sense the water vibrations ahead of its swimming line. Years of fighting for
existence in the sparse waters of the deep caves meant the fish could, and would,
eat anything digestible. Even its own eggs, as soon as spawning was over: the
lot disappeared rapidly down their throats.
Offering the fish different
recipes gave no choices, they ate everything, and if mixed with other, sighted,
species they beat them to the flakes at all levels of the aquarium. The idea of
using blind fish as a sensitive preference test for flavours of fish food was
The fish were found to be very hardy. When removed from the species
tanks to community groups it was noted that they accepted all water conditions,
from soft to hard, alkaline to acid, and could hold their own against all other
species. The harsh waters of the deep caves breed tough fishes.
pairs did reveal one problem. In their natural home the waters were hard and slightly
alkaline from the limestone that formed those stalagmites and stalactites. The
fry need this water chemistry or they develop osmosis problems. Hatching after
only two days they show a form of Dropsy as the fry swell and die if the water
is soft and acid.
An interesting fact is that the Blind Cave Fish fry look
like normal Characins, with two normal eyes! Within a few weeks however, folds
of fatty skin grow over the eyes and they disappear from view.
never develop any colour
of what use is colour if you are blind? The skin
is more than colourless; it is transparent, so the blood shows through to give
a meaty, fleshy look. However, years of breeding in tropical fish farms have produced
an odd effect - the skin is turning silvery. No doubt a genetic reaction to the
tropical sun. Perhaps this will eventually lead to The Blind Cave Fish being sighted
again - in a million years or so
Many Thanks to Dr
David Ford, http://www.drdavidford.pwp.blueyonder.co.uk/