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Sleep can be defined in birds and mammals by eye closure and typical electrical patterns in the neocortex, but fish lack eyelids and a neocortex. Yet this oscar is behaviorally quiescent at night, lying unresponsive on the bottom with its eyes turned downward, and might be said to sleep.
Amongst jawless fish, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. [6] Fish vision shows adaptation to their visual environment, for example deep sea fishes have eyes suited to the dark environment. Fish and other aquatic animals live in a different light environment than terrestrial species.
Sleep can follow a physiological or behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone (possibly with some exceptions; see below regarding the sleep of birds and of aquatic mammals), and a compensatory increase following deprivation of the state, this last known ...
Zangroniz said studies only use a few species of fish and don't represent the more than 30,000 fish species that exist. She added pain is measured in mammals on the grimace scale, often seen in ...
Usually, light enters through the fish eye at the cornea and passes through the pupil in order to reach the lens. Most fish species have a fixed size of the pupil while a few species have a muscular iris that allows for the adjustment of the pupil diameter. Fish eyes have a more spherical lens than other terrestrial vertebrates.
Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of interests. A special type of eye movement, rapid eye movement, occurs during REM sleep. The eyes are the visual organs of the human body, and move using a system of six muscles.
Dead fish have washed up on beaches. Florida's southwest coast experienced a flare-up of the toxic red tide algae this week, setting off concerns that it could continue to stick around for a while.
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