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Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
The yolk of a chicken egg Diagram of a fish egg; the yolk is the area which is marked 'C'. Among animals which produce eggs, the yolk (/ ˈ j oʊ k /; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo.
The first amniote egg – that is, a hard-shelled egg that could be laid on land, rather than remaining in water like the eggs of fish or amphibians – appeared around 312 million years ago. [6] In contrast, chickens are domesticated descendants of red junglefowl and probably arose little more than eight thousand years ago, at most.
A commercial chicken house with open sides raising broiler pullets for meat. Chickens farmed primarily for eggs are called layer hens. The UK alone consumes more than 34 million eggs per day. [84] Hens of some breeds can produce over 300 eggs per year; the highest authenticated rate of egg laying is 371 eggs in 364 days. [85]
Poultry meat and eggs provide nutritionally beneficial food containing protein of high quality. This is accompanied by low levels of fat which have a favourable mix of fatty acids. [70] Chicken meat contains about two to three times as much polyunsaturated fat as most types of red meat when measured by weight. [71]
A dual-purpose chicken is a type of chicken that may be used in the production of both eggs and meat. [42] In the past, many chicken breeds were selected for both functions. However, since the advent of laying and meat hybrids, industrial chicken breeding has made a sharp distinction between chickens with either function, [ 43 ] so that certain ...
Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.039 in). The eggs are generally surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish have thick, leathery coats, especially if ...
Egg white makes up around two-thirds of a chicken egg by weight. Water constitutes about 90% of this, with protein, trace minerals, fatty material, vitamins, and glucose contributing the remainder. [3] A raw U.S. large egg contains around 33 grams of egg white with 3.6 grams of protein, 0.24 grams of carbohydrate and 55 milligrams of sodium.