First cave dwelling callichthyid described!

WORDS: NATHAN HILL

It’s the Aspidoras you’ve never seen, and probably never will – but that cuts both ways! It lives in caves underground and lacks eyes, and for years it’s been described as the wrong fish. Now icthyologists Luiz Tencatt and Maria Bichuette have given it a name of its own. Meet Aspidoras mephisto, the first troglodont callichthyid.

In a paper published on March 1st, titled “Aspidoras mephisto, new species: The first troglobitic Callichthyidae (Teleostei: Siluriformes) from South America,” Tencatt and Bichuette explain how the fish, known for years as a cave-transitional form of Aspidoras albater turns out not to be that fish at all. Comparing multiple epigean (above ground) specimens with the hypogean (below ground) form, the duo was able to refute any claims of A. albater heritage.

What is it?

Aspidoras are the ‘little brothers’ of the Corydoradinae, physically smaller than their Corydoras and Scleromystax ilk. If you’ve dissected them and have microscopes to hand, then you can tell the difference by looking at bones in the skull – the supraoccipital fontanel to be exact.

If you’re not prone to pulling fish apart, then identify Aspidoras the way I do – if it’s smaller than a typical cory, has a longish body, and beady little eyes, it’s probably an Aspi.

Aspidoras mephisto takes the small eye thing a step further. Being a cave dweller, it has little use for vision, and so eye development is severely retarded. Unlike other well-known ‘cavies’ like the Mexican cavefish which just do away with eyes altogether, A. mephisto can come in many eye ‘flavours’. Where the eye is visible, it may or may not have a lens. It may be obscured by a shrunken orbit and skin growth closing over the top of it, or it may be covered altogether.

Its colours are mainly white-yellow or white-pink, but with a few translucent parts as well. It’s a distinctly washed out version of other Aspidoras, with grey brown blotches typical of the genus, black eyes and a green iridescence over the whole body. It’s subtly pretty.

 

Why the name?

Aspidoras is pretty meh as names go. ‘Aspis’ simply means shield, and ‘dora’ means skin, and it’s all a play on the armoured bodies these little cats have. Mephisto is a bit more fun, though. It comes from an old Germanic folklore demon, Mephistopheles, a character trapped in hell for selling his soul to Satan. If that name is derived from Hebrew, then it makes little sense to the fish (it kind of means ‘plasterer of lies’ in that translation), but if it’s of Greek origin, then it’s a literal negation of light loving – ‘me’ (negation, or not), ‘phos’ (light) and ‘philis’ (loving).

Short answer: it’s named after a demon. How cool?

Where does it live?

 

It’s only found in the Anesio-Russao cave system in the upper Rio Tocantins basin, Brazil. It lives in shallow (less than 50cm deep) slow moving waters, over substrates of boulders, clay and silt. The Anesio-Russao system is a limestone karst formation with outcrops all over the place though generally hidden by vegetation. It experiences a 5 or 6 month dry period followed by a wet season.

At the beginning of the dry season, water conditions there were: 7.8pH, conductivity 0.514mS.cm, dissolved oxygen 3.9mg/l, and temperature 22.3°C. By comparison, above ground at that time the water was softer (conductivity 0.248mS.cm), warmer (26.7°C) and more acidic (6.9pH).

It’s already threatened, courtesy of urban growth. Deforestation and sewage is impacting the caves, as well as the ever present South American mining enterprises.

It lives in pretty dense populations compared to other cave dwellers, with 5 or 6 individuals found in every square metre of footprint. There’s some root encroachment on their territory (they’re not necessarily deep down in the cave) and the juveniles use these roots for cover.

Like other callichthyds, they forage about in the substrates at about a 60° angle.

Are they blind?

Some are, some aren’t. A lot depends on the level of eye regression, but it’s interesting to note that they’re either unsighted or unruffled – they showed no aversion to lamps in the caves, nor the observers watching them. As already mentioned, the eyes can be at various stages of regression, but how much they even use them is open to some debate. 

Live uncatalogued specimen of Aspidoras mephisto  from the Anésio III cave, Posse, Goiás, Brazil. Image copyright Danté Fenolio.

How big are they?

Tiny, like other Aspidoras. The holotype of the species is 45.6mm long, and it appears the size ranges for adults caught vary from 18.8mm to 45.6mm.

A curious offshoot of troglodont lifestyles is longevity, and A. mephisto seems to be no exception. The captive holotype (retrospectively identified – they’d have been honorary A. albater before) caught as an adult back on April 7th, 2007 stayed alive until its preservation in April 2016 – a nine year minimum adult lifespan!

 

How rare are they?

Tencatt and Bichuette propose that the fish should be considered Endangered already, for a few reasons. They’re only known from 5 locations over a 500km2 area, and the habitat they’re known to be is showing gradual decrease from encroachment.

The presence of sewage affecting the caves, and a lack of legal protection for them, both suggest that A. mephisto could easily shift into the Critically Endangered category real soon.

How rare are they in the hobby? You’re not going to see them any time soon, that’s for sure. 

Want to know more?

If you’re the kind of person who loves scientific papers, then you can find the original below. If words like ‘sphenotic’, 'epiphesial’, and ‘ceratobranchial’ get you excited then go have your fill. It isn’t light bedtime reading, but the images are pretty cool.

Aspidoras link right here!

Photo credits: Danté Fenolio, Luiz Fernando Caserta Tencatt, Maria Elina Bichuette, PLOS one and Creative Commons.