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Blind as a Cave Fish
By Dr David Ford, Consultant to Aquarian®, member of Halifax AS

Who needs Eyes?

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 of generations.

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.

All 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 would see.

Pot-hole Collectors

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.

After wading 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.

What's 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.

My Experience

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 abandoned!

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.

Breeding 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.

The fish 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….