A large part of ichthyology’s fascination is the spectacular and unusual nature of the subject matter . As a few examples:
●Coelacanths, an offshoot of the lineage that gave riseto the amphibians, were thought to have died out with the dinosaurs at the end of the Cretaceous, 65 million years ago. However, in 1938, fishermen in South Africa trawled up a very live Coelacanth. This fortuitous capture of a living fossil not only rekindled debates about the evolution of higher vertebrates, but underscored the international and political nature of conservation efforts.
●Lungfishes can live in a state of dry “suspended animation” for up to 4 years, becoming dormant when their ponds dry up and reviving quickly when immersed in water.
●Antarctic fishes live in water that is colder than the freezing point of their blood. The fishes keep from freezing by avoiding free ice and because their blood contains antifreeze proteins that depress their blood’s freezing point to −2°C. Some Antarctic fishes have no hemoglobin.
●Deepsea fishes include many forms that can swallow prey larger than themselves. Some deepsea angler fishes are characterized by females that are 10 times larger than males, the males existing as small parasites permanently fused to the side of the female, living off her blood stream.
●Fishes grow throughout their lives, changing their ecological role several times. In some fishes, differences between larvae and adults are so pronounced that many larvae were originally described as entirely different taxa.
●Fishes have maximum life spans of as little as 10weeks (African killifishes and Great Barrier Reefpygmy gobies) and as long as 150 years (sturgeons andscorpaenid rockfishes). Some short-lived species are annuals, surviving drought as eggs which hatch with the advent of rains. Longer lived species may not begin reproducing until they are 20 years old, and then only at 5+year intervals.
●Gender change is common among fishes. Some species are simultaneously male and female, whereas others change from male to female, or from female to male.
●Fishes engage in parental care that ranges from simplenest guarding to mouth brooding to the production of external or internal body substances upon which young feed. Many sharks have a placental structure as complex as any found in mammals. Egg-laying fishes may construct nests by themselves, whereas some species deposit eggs in the siphon of living clams, on the undersides of leaves of terrestrial plants, or in thenests of other fishes.
●Fishes are unique among organisms with respect to the use of bioelectricity. Many fishes can detect biologically meaningful, minute quantities of electricity, which they use to find prey, competitors, orpredators and for navigation. Some groups have converged on the ability to produce an electrical field and obtain information about their surroundings from disturbances to the field, whereas others produce large amounts of high-voltage electricity to deter predatorsor stun prey.
●Fishes are unique among vertebrates in their ability to produce light; this ability has evolved independently indifferent lineages and can be either autogenic(produced by the fish itself) or symbiotic (produced by bacteria living on or in the fish).
●Although classically thought of as cold-blooded, some pelagic sharks and tunas maintain body temperatures warmer than their surroundings and have circulatory systems specifically designed for such temperature maintenance.
●Predatory tactics include attracting prey with modified body parts disguised as lures, or by feigning death. Fishes include specialists that feed on ectoparasites,feces, blood, fins, scales, young, and eyes of other fishes.
●Fishes can significantly change the depth of their bodies by erecting their fins or by filling themselves with water, an effective technique for deterring many predators. In turn, the ligament us and levering arrangement of mouth bones in some fishes allows them to increase mouth volume when open by as much as 40-fold.
●Some of the most dramatic field and laboratory demonstrations of evolution as an ongoing process result from studies of fishes. Both natural and sexual selection have been experimentally manipulated in Guppies, swordtails, and sticklebacks, among others. These investigations show how competition, predation, and mate choice lead to adaptive alterations in body
shape and armor, body color and color vision, and feeding habits and locales. Fishing has also proven to be a powerful evolutionary force, affecting population structure and size, ages and sizes at which fish reproduce, body shape, and behavior.
Additionally, and although not covered in detail in this text, fishes have become increasingly important as laboratory and assay organisms. Because of small size, ease of care, rapid growth and short generation times, and larval anatomical features, such species as Medaka, Oryzias latipes,and Zebrafish, Danio rerio, are used increasingly in studies of toxicology, pharmacology, neurobiology, developmental biology, cancer and other medical research, aging, genomics, and recombinant DNA methodology (e.g., Geisler et al.1999; Bolis et al. 2001; Tropepe & Sive 2003; Zbikowska2003).
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