Vision In Fish
Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals (including humans) normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarised light. Among jawless fishes, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate, were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Fish vision shows evolutionary a ...
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Astronotus Ocellatus - Closeup (aka)
''Astronotus'' is a genus of South American fish from the family Cichlidae. There are two commonly recognized species in the genus (listed below), though genetic evidence suggests that additional species exist; several of these possibly distinct populations also have very different juvenile coloration from the two recognized species. Both of the commonly recognized species are found in the Amazon Basin, while one of two also is found in the Paraná River, Paraná and Paraguay River, Paraguay rivers. ''Astronotus'' species grow to 35 cm in size, and are Monomorphism (biology), monomorphic. They are opportunistic omnivores and consume a range of smaller fish, fruits, nuts, crustaceans, mollusks and other invertebrates in the wild. One species, the Oscar (fish), oscar (''Astronotus ocellatus''), is popular in the aquarium trade. ''A. ocellatus'' forms monogamous pairs which spawn in the open, typically on a flattened stone or in a shallow depression. The juvenile colouration is ...
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Polarised Light
Polarization ( also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string ''(see image)''; for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids. An electromagnetic w ...
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