Swati Basu Das heads deep into the caverns of Al Hoota Cave to glimpse into the dark yet vibrantly sensory world of one of the planet’s evolutionary marvels – the Oman garra.
What survives in the dark does so because its’ very being has adapted to thrive in ways we might find unfathomable. If this thought disturbs you, rightly so – as it plants a seed of doubt about our own fragility when faced with adverse conditions.
If necessity is the mother of invention, then adaptation is its by-product. Proof positive can be found deep in the subterranean waters of Al Hamra’s Al Hoota Cave, where an unassuming species of fish continues to validate Charles Darwin’s theory of ‘survival of the fittest’.
Adapted impeccably to its environment, this unique population of Oman garra – or ‘garra barreimiae’ is better known as the ‘Omani blind fish’. With its sightless eyes and striking loss of pigmentation, these almost translucent ray-finned fish have acclimated to the most extreme conditions of darkness over the centuries.
An endemic species in the Sultanate and parts of the UAE, it’s only here in Al Hoota Cave where an enclave of the species has transformed their very nature to their surroundings, making them an exceptional instance of evolution at play – with their altered traits circulated even among their off-spring.
Two million-years-old, Al Hoota Cave has a fascinating ecosystem, and the blind fish found in the underground lake of this cave chamber are a distinctive natural wonder.
“The blind fish are found only in Oman in the entire region,” says Ibrahim Said Al Wahabi, Asset Manager, OMRAN. “A native to the underground lake of Al Hoota Cave, this species forms an important part of the cave ecosystem – apart from its fascinating rock formations. It’s nothing less than a marvel to a fish with no eyes. The lake is pitch black, and the fish have adapted themselves to such conditions. The cave was opened to tourists in 2006 and it has a unique ecosystem. The cave is five kilometres long and has three entrances. The lake in it is formed by flood water, and the blind fish dwelling in this water are a major tourist attraction, as they breed inside the lake.”
Lacking external eyes, their tightly fused eyelids resemble a milky blotch, and scientists believe that their blindness, altered pigmentation, and translucent scales developed over hundreds of years. It’s also believed that these blind cave fish are the same species of garra found in abundance in fresh falaj water. Researchers believe that the same school of fish that once shoaled through the falaj creeks may have ended up trapped in the natural cistern of Al Hoota Cave.
“The species is similar to the one we see in the wadi stream,” explains Sergey Dobretsov, Director of the Centre of Excellence in Marine Biotechnology at Sultan Qaboos University. “Due to the flow of water, the fish might have entered the cave system through narrow crevices. Blindness doesn’t occur in a day or two, as the evolution takes several hundred years in the absence of sunlight. The lack of light not only makes them blind but in the process of transformation, they lose their pigmentation. Their scales shed all colour and become transparent.”
And thus, the evolutionary journey of the Omani blind cave fish begins in the unlit lake-water of Al Hoota Cave. With little choice but either to adapt to the blackness, or die, they have ingeniously allowed evolution to take away their sight – but not their life; ultimately helping them to survive.
“Over time, to save their energy in the dark, they avoided using certain body parts. In this case, it was their eyes,” says Dr. Dobretsov. “Saving energy in the dark is the prime reason behind the shutting the eyelids – and blindness is now the source of their energy. Although sightless, these cave fish can still sense danger and feel the obstacles around them.”
But the marvel of their existence lies in how species without vision, in complete darkness, sustain themselves. Yet these underground cave-dwellers are adept in the dark environment of the cave and nibble on whatever they encounter – having adapted skillfully in an atmosphere where there is no sufficient food source and the oxygen level is low.
To this, Dr. Dobretsov states: “They use their sensors, their nose, and even their scales to sense food around them. Food is scarce in a cave chamber, so they eat almost anything and everything that comes their way.”
A few blind fish on display in the museum at Al Hoota are said to regain their eyesight when exposed to light for several days.
“This transformation is natural,” says Abdul Rahman Maktoom Jaber Al Hinai, Maintenance Manager, Al Hoota Cave. “A source of light helps them recover their vision, but when we return them to the lake, they turn blind. Therefore, we ensure to keep the lake area unexposed to any harsh light and let the phenomenon of evolution continue.”
Stepping down the endless stairs to Al Hoota’s underground lake, it takes a minute or two for our own eyes to adapt to darkened conditions. It’s only after some time that we can see them, translucent arrows cutting through the pitch-black waters, survivors by choice, selected by nature.