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A bathtub faucet with built-up calcification from hard water in Southern Arizona. Hard water is water that has a high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, [1] which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates.
A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits.Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians.
The bishop-fish, a piscine humanoid reported in Poland in the 16th century. Aquatic humanoids appear in legend and fiction. [1] "Water-dwelling people with fully human, fish-tailed or other compound physiques feature in the mythologies and folklore of maritime, lacustrine and riverine societies across the planet." [2]: 6
The few characteristics they share with the latter are now considered as primitive for all vertebrates. Around the start of the Devonian, fish started appearing with a deep remodelling of the vertebrate skull that resulted in a jaw. [323] All vertebrate jaws, including the human jaw, have evolved from these early fish jaws.
Seafood is any form of sea life regarded as food by humans. It prominently includes shellfish, and roe. Shellfish include various species of molluscs, crustaceans, and echinoderms. In most parts of the world, fish are generally not considered seafood even if they are from the sea.
Early bony fish had simple respiratory diverticula (an outpouching on either side of the esophagus) which helped them breathe air in low-oxygen water as a form of supplementary enteral respiration. In ray-finned fish these have evolved into swim bladders, the changing sizes of which help to alter the body's specific density and buoyancy.
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ in bony fish (but not cartilaginous fish [1]) that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift via swimming, which expends more energy. [2]
Chimaeras also have some characteristics of bony fishes. A renewed effort to explore deep water and to undertake taxonomic analysis of specimens in museum collections led to a boom during the first decade of the 21st century in the number of new species identified. [2] A preliminary study found 8% of species to be threatened. [14]