According to the researchers, fish usually sense water flow with neuromasts, which are small organs in their lateral lines comparable to the human ear. As they have to adapt to life in the darkness, cavefish typically have an enlarged neuromast system.?? However, the researchers found that the Astroblepus pholeter, a cave-dwelling catfish, has surprisingly few neuromasts.
This particular cavefish lives in complete darkness in a cave, located at the base of a cloud forest, through which a rapidly flowing stream passes. In order to navigate in this extreme environment, the fish shows a hypertrophy of skin denticles, structures that are composed of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel, which are used mostly for cutting or protection in other fishes. The skin teeth of the A. pholeter are connected to the fish's mechanosensory part of the brain, allowing them to detect the direction of water flow and the distance, the study revealed.
"We found a new way in which evolution has allowed animals to live in this challenging environment and we now have a whole new sensory organ to examine when we find new species," said Daphne Soares, assistant professor at the University of Maryland's Department of Biology. ??The researchers suggest that the rapidly flowing and turbulent stream in the cave may be responsible for this evolution, as the current may be too strong for the neuromast system to develop. In behavioral trials, they observed that fish with their denticles removed could not orient in flowing water or cling to rocks along the bottom.
The study was conducted by researchers at the University of Maryland in collaboration with the National Institutes of Health and the Pontificia Universidad Católica del Ecuador. It was published in the August issue of the Current Biology journal.
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