World’s largest cave fish species found in Meghalaya
The world’s largest species of cave fish measuring over 40cm or around one and a half feet in length have been found inside a remote cave in Meghalaya’s Jaintia Hills.
Details of the find have been published in an article by four researchers in the November 2019 issue of Cave and Karst Science, a journal published by the British Cave Research Association.
The fish, related to the Golden Mahseer but has no eyes and is white due to lack of melanin pigmentation, was found in a cave located in a remote and densely forested area in Jaintia Hills region of Meghalaya by a team of international and local researchers in February last year.
There are 250 known species of fish found under the earth’s surface. As they live in a nutrient-limited environment most of these species are small—195 of them have a mean length of 8.5cm. The only two species, which exceed 30cm, are eel-like and have very thin bodies.
“It has always been assumed that cave fishes exceeding 350mm (35cm) would be most unlikely on resource grounds but this has now been shown to be spectacularly wrong,” said the article.
“The fish discovered in Meghalaya in February 2019 is not only substantially longer than the longest previously known species but is considerably more bulky with a body mass likely to exceed that of the next largest cave fish by at least an order of magnitude,” it added.
Meghalaya has an elaborate and extensive network of caves. Several international and Indian researchers have been mapping the caves since 1992 in association with Meghalaya Adventurers Association and the latest find is part of that project.
The researchers had found a similar fish in 1998 as well, inside a cave located 8km away from the present location, but they were not able to take clear photos or capture the fish back then.
Many of the fish were found in small pools located deep inside the cave. There was evidence that the caves get flooded during the rainy season.
Researchers believe the fish is bulky in size due to large and regular food supply, with surface vegetation entering the cave through the entrance shaft on rainy seasons. There appeared to be hundreds of similar fish in the cave.
“When first encountered the fish appeared unresponsive to light, although they did react to the water disturbance created by the cavers wading through the pools,” the article said.
“Although it seems that they were initially unresponsive to light, they are certainly able to perceive light,” it added noting that the fishes initially showed no reaction to light for the first time but moved away when torchlight was shone on them again later.
The researchers stated that the Meghalaya cave fish is a close anatomical match to ‘Tor putitora’ (Golden Mahseer), which is found widely in the area. But “it is highly likely that genetically they are somewhat different from this species” as a result of isolated evolution (it lacks eyes and melanin pigmentation).
“The fish discovered in the Jaintia Hills of Meghalaya in February 2019 is by far the largest troglobitic fish yet known, and is nearly 5 times the mean length (85 mm/8.5 cm) of all known subterranean fishes to date,” the article concluded.