Meet the Al Hoota Cave dwellers: our fascinating fish

In this cave-dwelling population, eyes are present in juveniles, but become covered in older fish, although individuals artificially exposed to light show increased development of the optic lobe in the brain…

There was great excitement when, in 1980, very rare, blind fish were found living in the large central lake of Al Hoota Cave. They belong to an incredible species – Garra barreimaie – found only in Oman, UAE and Bahrain which are able to survive the arid conditions of the region. Al Hoota’s distinct cave-dwelling population are even more rare and interesting as they have adapted to their dark environment by losing their pigment, some of their scales and even their external eyes. Although they are born with eyes these are covered over as they age and the mature fish have no optic function at all. Amazing

Would you like to know more? This is what the scientists say:

The blind fish is a bottom-dwelling species, often hiding under stones or in crevices and nuzzling over gravel and rock surfaces in a catfish-like manner. Juveniles tend to be more active, but all dart about frenetically when approached in a shallow pool, where predation risk may be high. The species has a tendency to move upstream, a behaviour which may aid dispersal when the Wadis flow after rain. Individuals have been observed to climb several meters up waterfalls, and can even travel short distances out of water, moving across damp rock surfaces. The blind fish feeds on detritus and algae, and will sometimes cannibalise its own eggs. Larger individuals appear to maintain a temporary territory, within which the fish forages and chases away intruders.

Small and dark in colour, the blind cave fish is typically mottled brown, sometimes with more colourful red, white or blue markings in larger adults, and has a thin, pale transverse line just behind the head, appearing to demarcate the head from the body. The body is relatively long, with a rather flat underside, and the head is wedge-shaped, with a blunt snout and a specialised mouth plate on the underside, which acts as a suction device. The scales are large and heavy.

Little is known about the life history of the blind fish, although it is thought to lay tiny eggs in gravel, the eggs apparently able to hatch within 24 hours, but said to hatch only when conditions are favourable. Spawning may be triggered by rain or thunderstorms, which would ensure the rapid dispersal of the eggs. The cave-dwelling form is likely to feed on detritus washed into the cave, and possibly on bat guano and small invertebrates. Like other cave fish, it may live longer than surface-dwelling individuals, and also shows other behavioural adaptations to underground life, such as a reduced tendency to form shoals, probably due to a reduced predation risk. There is evidence that, despite its lack of eyes, the cave form has retained some ability to respond to light.