New research involving eyeless fish revealed how highly-developed visual systems in the animal kingdom take a surprising toll on vital organs.

A team of scientists looked at Mexican cavefish, and determined visual systems can require between 5 percent and 15 percent of an animal's total energy budget, Lund University reported.Big brains and advanced nervous systems can only develop in environments where the required energy consumption is possible, such as those containing adequate nutrients.  

In the past there have been few concrete measures of how high the energy cost of a nervous system. These new findings were made by focusing on a cavefish that lost its visual system through regression, but has a surface-dwelling variant of the same species. The surface-dwelling morph has large eyes, but also has a greater access to food then its cave-dwelling peer.

"Our measurements in the Mexican cavefish show that the visual system requires between 5 [percent] and 15 [percent] of the animal's total energy budget, depending on the age of the fish. This is a tremendously high cost! Over evolution, this morph lost both eyes and visual cortex, without a doubt because of the unsustainable energy cost of maintaining a sensory system that no longer had any significance," said Damian Moran, one of the researchers with the study.

The amount of energy required to support the surface-dwelling species' visual system was surprisingly high, and researchers hope the findings will help them better-understand how selective pressure works in the evolutionary process.

"Animals with large and well-developed eyes, necessary for their survival, pay a high price for them. As all animals have a strictly limited energy budget, a major investment in the visual system only occurs at a cost to other organ systems," said Eric Warrant, researcher in Functional Zoology at Lund University.

The findings were published in a recent edition of the journal Science Advances.