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However, other fish do seem to sleep, especially when purely behavioral criteria are used to define sleep. For example, zebrafish , [ 6 ] tilapia , [ 7 ] tench , [ 8 ] brown bullhead , [ 9 ] and swell shark [ 10 ] become motionless and unresponsive at night (or by day, in the case of the swell shark); Spanish hogfish and blue-headed wrasse can ...
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 ...
Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked.
A large group of yellowfin tuna swimming off the coast of Italy. Like all fish, they sleep, but it's not like human sleep. Giordano Cipriani/The Image Bank via Getty Images Curious Kids is a ...
The upper jaw teeth of the sleeper shark are spike-like, while the lower jaw teeth are oblique cusps and overlapping bases. This arrangement allows grasping and sawing of food too large to swallow. Pacific sleeper sharks have a short caudal fin, which allows them to store energy for fast and violent bursts of energy to catch prey. [8]
The southern sleeper shark feeds primarily on cephalopods, especially squid — including the giant and colossal squids — and numerous fishes.Documented stomach contents of individual sleeper sharks have also, albeit infrequently, contained the remains of marine mammals or seabirds, possibly as a result of scavenging on sunken carcasses or whale falls. [1]
Zebra sharks are nocturnal and spend most of the day resting motionless on the sea floor. At night, they actively hunt for molluscs, crustaceans, small bony fishes, and possibly sea snakes inside holes and crevices in the reef. Though solitary for most of the year, they form large seasonal aggregations.
Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring 1 m (3.3 ft) in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines ...