Sleep is a behavior pervasive throughout the animal kingdom. It is usually characterized by persistent immobility and decreased responsiveness.
Despite the underlying impairment of sleep, its persistence over evolutionary time indicates that it performs one or more essential functions. One hypothesis for such a basic function is that Sleep conserves energy by promoting rest and slowing the metabolic rate relative to wakefulness.
. has been reported Energy saving during sleep in different animalsincluding humans, cats, rats, birds, and fruit flies, but it was not known whether the reduced energy intake also occurred while the fish were sleeping.
A study conducted by a group of researchers from scientific institutions in Australia showed that sharks do this Maintain periods of sleep in order to conserve their energy.
The research led by Michael Kelly of the University of Western Australia has seven chess sharks From the Hauraki Gulf, in northeastern New Zealand, they are housed in outdoor aquariums under natural light conditions. Animals were fed a sardine diet and maintained for a minimum of 2 weeks prior to the start of the experiments. Food was withheld for at least 48 h before the start of the experiments to ensure that the animals reached a post-absorption state.
After that period, these chess sharks (which got their name Because the color pattern of the dark spots on their skin resembles a checkerboard) They were individually placed in a sealed spirometry chamber. Intermittent flow spirometry and video recordings After 48 hours to allow each animal to acclimatize to its new conditions before beginning data collection. Then, each protocol continued for 24 hours in which they were exposed to 12 hours of light and 12 hours of darkness.
During that time they were evaluating Changes in the rate of oxygen consumption With the aim of determining whether sleep is a limiting factor in energy conservation in cold-blooded vertebrates.
Eye conditions were scored as open or closed and inactive shark body positions were assessed as flat (lying on tank bottom) or upright (sitting on pectoral fins). While the sharks kept their eyes open while swimming, they discovered that during the sleep state these animals’ eyes remained closed.
Activity states were categorized as swimming, resting (inactive less than 5 min), or sleeping (inactive more than 5 min). The study revealed that the sharks’ oxygen levels were significantly lower during their sleep period, which lasted about 5 minutes. Other signs that they are sleeping are that during the period of activity of the animals, i.e. When they were swimming, high levels of oxygen were recorded.
With regard to the position of their bodies, scientists have noticed that during their sleep they take a flat body position, in contrast to when they were at rest, where they remained erect. Thanks to this study, the old theory that was asserting that sharks do not sleep has been demolished.