Among animals which produce one, the yolk is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some kinds of egg contain no yolk, for example because they are laid in situations where the food supply is sufficient or because the embryo develops in the parent's body, which supplies the food through a placenta. Reproductive systems in which the mother's body supplies the embryo directly are said to be matrotrophic. In many species, such as all birds, most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals very small species such as some fishes and invertebrates, the yolk material is not in a special organ, but inside the ovum; as stored food, yolks are rich in vitamins, minerals and proteins. The proteins function as food in their own right, in controlling the storage and supply of the other nutrients. For example, in some species the amount of yolk in an egg cell affects the developmental processes that follow fertilization.
The yolk is not living cell material like protoplasm, but passive material, to say deutoplasm. The food material and associated control structures are supplied during oogenesis; some of the material is stored more or less in the form in which the maternal body supplied it as processed by dedicated non-germ tissues in the egg, while part of the biosynthetic processing into its final form happens in the oocyte itself. Apart from animals, other organisms, like algae, specially in the oogamous, can accumulate resources in their female gametes. In gymnosperms, the remains of the female gametophyte serve as food supply, in flowering plants, the endosperm. In the avian egg, the yolk is a hue of yellow in color, it is spherical and is suspended in the egg white by one or two spiral bands of tissue called the chalazae. The yolk mass, together with the egg cell or ovum properly are enclosed by the vitelline membrane, whose structure is different from a cell membrane; the yolk is extracellular to the oolemma, being not accumulated inside the cytoplasm of the egg cell, contrary to the claim that the avian egg cell and its yolk are a single giant cell.
After the fertilization, the cleavage of the embryo leads to the formation of the germinal disc. As food, the chicken egg yolk is a major source of minerals, it contains all of the egg's fat and cholesterol, nearly half of the protein. If left intact when an egg is fried, the yellow yolk surrounded by a flat blob of egg white creates a distinctive "sunny-side up" form. Mixing the two components together before cooking results in a pale yellow mass, as in omelets and scrambled eggs; the developing embryo inside the egg uses the yolk as sustenance. It is at times separated from the egg white for cooking, is employed as an emulsifier, is used in mayonnaise, hollandaise sauce, crème brûlée, ovos moles, it is used in painting as a component of traditional egg-tempera. It is used in the production of egg-yolk agar plate medium, useful in testing for the presence of Clostridium perfringens. Egg yolk contains; the antibody transfers from the laying hen to the egg yolk by passive immunity to protect both embryo and hatchling from microorganism invasion.
Egg yolk can be used to make liqueurs such as eggnog. Egg yolk is used to extract egg oil which has various cosmetic and medicinal uses; the yolk makes up about 33% of the liquid weight of the egg. The yolk of one large egg (56.7 g total, 17.6 g yolk. All of the fat-soluble vitamins are found in the egg yolk. Egg yolk is one of the few foods containing vitamin D; the composition of the most prevalent fatty acids in egg yolk is: Unsaturated fatty acids: Oleic acid, 47% Linoleic acid, 16% Palmitoleic acid, 5% Linolenic acid, 2% Saturated fatty acids: Palmitic acid, 23% Stearic acid, 4% Myristic acid, 1%Egg yolk is a source of lecithin, as well as egg oil, for cosmetic and pharmaceutical applications. Based on weight, egg yolk contains about 9% lecithin; the yellow color is due to lutein and zeaxanthin, which are yellow or orange carotenoids known as xanthophylls. The different yolk's proteins have distinct roles. Phosvitins are important in sequestering calcium and other cations for the developing embryo.
Phosvitins are one of the most phosphorylated proteins in nature. Lipovitellins are involved in lipid and metal storage, contain a heterogeneous mixture of about 16% noncovalently bound lipid, most being phospholipid. Lipovitellin-1 contains two chains, LV1N and LV1C. Yolks hold more than 90% of the calcium, phosphorus, thiamine, vitamin B6, vitamin B12, pantothenic acid of the egg. In addition, yolks cover all of the fat-soluble vitamins: A, D, E, K in the egg, as well as all of the essential fatty acids. A single yolk from a large egg contains 22 mg of calcium, 66 mg of phosphorus, 9.5 micrograms of selenium, 19 mg of potassium, according to the USDA. Double-yolk eggs occur when ovulation occurs too or when one yolk becomes joined with another yolk; these eggs may be the result of a young hen's reproductive cyc
A snout is the protruding portion of an animal's face, consisting of its nose and jaw. In many animals, the equivalent structure is called rostrum, or proboscis; the wet furless surface around the nostrils of the nose of some animals is called the rhinarium. The rhinarium is associated with a stronger sense of olfaction; the snout is considered a weak point on most animals: because of its structure, an animal can be stunned or knocked out, or have its snout snapped by applying sufficient force. Snouts are found on many mammals in a variety of shapes; some animals, including ursines and great cats, have box-like snouts, while others, like shrews, have pointed snouts. Pig snouts are cylindrical; the muzzle begins at the stop, just below the eyes, includes the dog's nose and mouth. In the domestic dog, most of the upper muzzle contains organs for detecting scents; the loose flaps of skin on the sides of the upper muzzle that hang to different lengths over the mouth are called flews. It is innervated by one of the twelve pairs of cranial nerves.
These nerves emerge through the skull to their target organs. Other destinations of these nerves are eyeballs and tongue; the muzzle shape of a domestic dog ranges in shape depending upon the breed, from long and thin, as in the Rough Collie, to nearly nonexistent because it is so flat, as in the Pug. Some breeds, such as many sled dogs and Spitz types, have muzzles that somewhat resemble the original wolf's in size and shape, others in the less extreme range have shortened it somewhat as in many hounds
Gillnetting is a common fishing method used by commercial and artisanal fishers of all the oceans and in some freshwater and estuary areas. Gill nets are composed of vertical panels of netting that hang from a line with spaced floaters that hold the line on the surface of the water; the floats are sometimes called "corks" and the line with corks is referred to as a "cork line." The line along the bottom of the panels is weighted. Traditionally this line has been weighted with lead and may be referred to as "lead line." A gill net is set in a straight line. Gill nets can be characterized by mesh size, as well as colour and type of filament from which they are made. Fish may be caught by gill nets in three ways: Wedged – held by the mesh around the body. Gilled – held by mesh slipping behind the opercula. Tangled – held by teeth, maxillaries, or other protrusions without the body penetrating the mesh. Most fish are gilled. A fish passes only part way through the mesh; when it struggles to free itself, the twine prevents escape.
Gillnets are so effective that their use is monitored and regulated by fisheries management and enforcement agencies. Mesh size, twine strength, as well as net length and depth are all regulated to reduce bycatch of non-target species. Gillnets have a high degree of size selectivity. Most salmon fisheries in particular have an low incidence of catching non-target species. A fishing vessel rigged to fish by gillnetting is a gillnetter. A gillnetter which deploys its gillnet from the bow is a bowpicker, while one which deploys its gillnet from the stern is a sternpicker. Gillnets existed in ancient times. In North America, Native American fishermen used cedar canoes and natural fibre nets, e.g. made with nettles or the inner bark of cedar. They would attach stones to the bottom of the nets as weights, pieces of wood to the top, to use as floats; this allowed the net to suspend straight down in the water. Each net would be suspended either between two boats. Native fishers in the Pacific Northwest and Alaska still use gillnets in their fisheries for salmon and steelhead.
Both drift gillnets and setnets have long been used by cultures around the world. There is evidence of fisheries exploitation, including gillnetting, going far back in Japanese history, with many specific details available from the Edo period. Fisheries in the Shetland Islands, which were settled by Norsemen during the Viking age, share cultural and technological similarities with Norwegian fisheries, including gillnet fisheries for herring. Many of the Norwegian immigrant fishermen who came to fish in the great Columbia River salmon fishery during the second half of the 19th century did so because they had experience in the gillnet fishery for cod in the waters surrounding the Lofoten Islands of northern Norway. Gillnets were used as part of the seasonal round by Swedish fishermen as well. Welsh and English fishermen gillnetted for Atlantic salmon in the rivers of Wales and England in coracles, using hand-made nets, for at least several centuries; these a few of the examples of historic gillnet fisheries around the world.
Gillnetting was an early fishing technology in colonial America, used for example, in fisheries for Atlantic salmon and shad. Immigrant fishermen from northern Europe and the Mediterranean brought a number of different adaptations of the technology from their respective homelands with them to the expanding salmon fisheries of the Columbia River from the 1860s onward; the boats used by these fisherman were around 25 feet long and powered by oars. Many of these boats had small sails and were called "row-sail" boats. At the beginning of the 1900s, steam powered ships would haul these smaller boats to their fishing grounds and retrieve them at the end of each day. However, at that time gas powered boats were beginning to make their appearance, by the 1930s, the row-sail boat had disappeared, except in Bristol Bay, where motors were prohibited in the gillnet fishery by territorial law until 1951. In 1931, the first powered drum was created by Laurie Jarelainen; the drum is a circular device, set to the side of the boat and draws in the nets.
The powered drum allowed the nets to be drawn in much faster and along with the faster gas powered boats, fisherman were able to fish in areas they had been unable to go into, thereby revolutionizing the fishing industry. During World War II, navigation and communication devices, as well as many other forms of maritime equipment were improved and made more compact; these devices became much more accessible to the average fisherman, thus making their range and mobility larger. It served to make the industry much more competitive, as the fisherman were forced to invest more in boats and equipment to stay current with developing technology; the introduction of fine synthetic fibres such as nylon in the construction of fishing gear during the 1960s marked an expansion in the commercial use of gillnets. The new materials were cheaper and easier to handle, lasted longer and required less maintenance than natural fibres. In addition, multifilament nylon, monofilament or multimonofilament fibres become invisible in water, so nets made with synthetic twines caught greater numbers of fish than natural fibre nets used in comparable situations.
Nylon is resistant to abrasion and degradation, hence the netting has the potential to last for many years if it is not recovered. This ghost fishing is of environmental concern. Attaching the gillnet floats with biodegradable mat
An estuary is a enclosed coastal body of brackish water with one or more rivers or streams flowing into it, with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments, they are subject both to marine influences—such as tides and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The mixing of sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are classified according to their geomorphological features or to water-circulation patterns, they can have many different names, such as bays, lagoons, inlets, or sounds, although some of these water bodies do not meet the above definition of an estuary and may be saline.
The banks of many estuaries are amongst the most populated areas of the world, with about 60% of the world's population living along estuaries and the coast. As a result, many estuaries suffer degradation from a variety of factors including: sedimentation from soil erosion from deforestation and other poor farming practices; the word "estuary" is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus, meaning tide. There have been many definitions proposed to describe an estuary; the most accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, within which sea water is measurably diluted with freshwater derived from land drainage". However, this definition excludes a number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff.
This broad definition includes fjords, river mouths, tidal creeks. An estuary is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides; the sea water entering the estuary streams. The pattern of dilution varies between different estuaries and depends on the volume of fresh water, the tidal range, the extent of evaporation of the water in the estuary. Drowned river valleys are known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley; this is the most common type of estuary in temperate climates. Well-studied estuaries include the Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border; the width-to-depth ratio of these estuaries is large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths exceed 30 m.
Examples of this type of estuary in the U. S. are the Hudson River, Chesapeake Bay, Delaware Bay along the Mid-Atlantic coast, Galveston Bay and Tampa Bay along the Gulf Coast. Bar-built estuaries are found in place where the deposition of sediment has kept pace with rising sea level so that the estuaries are shallow and separated from the sea by sand spits or barrier islands, they are common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches. Formation of barrier beaches encloses the estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries develop on sloping plains located along tectonically stable edges of continents and marginal sea coasts, they are extensive along the Atlantic and Gulf coasts of the U. S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m. The barrier beaches that enclose bar-built estuaries have been developed in several ways: building up of offshore bars by wave action, in which sand from the sea floor is deposited in elongated bars parallel to the shoreline, reworking of sediment discharge from rivers by wave and wind action into beaches, overwash flats, dunes, engulfment of mainland beach ridges due to sea level rise and resulting in the breaching of the ridges and flooding of the coastal lowlands, forming shallow lagoons, elongation of barrier spits from the erosion of headlands due to the action of longshore currents, with the spits growing in the direction of the littoral drift.
Barrier beaches form in shallow water and are parallel to the shoreline, resulting in long, narrow estuaries. The average water depth is less than 5 m, exceeds 10 m. Examples of bar-built estuaries are Barnegat Bay, New Jersey. Fjords were formed where pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross s
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals carnivores use teeth for hunting or for defensive purposes; the roots of teeth are covered by gums. Teeth hardness; the cellular tissues that become teeth originate from the embryonic germ layer, the ectoderm. The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position; the teeth of mammals have deep roots, this pattern is found in some fish, in crocodilians. In most teleost fish, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw; some animals develop only one set of teeth. Sharks, for example, grow a new set of teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain constant length.
The industry of the beaver is due in part to this qualification. Many rodents such as voles and guinea pigs, but not mice, as well as leporidae like rabbits, have continuously growing molars in addition to incisors. Teeth are not always attached to the jaw. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper; some teleosts have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are identical in structure and are to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of vertebrates' teeth.
Living amphibians have small teeth, or none at all, since they feed only on soft foods. In reptiles, teeth are simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes; the pattern of incisors, canines and molars is found only in mammals, to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary between species; the genes governing tooth development in mammals are homologous to those involved in the development of fish scales. Study of a tooth plate of a fossil of the extinct fish Romundina stellina showed that the teeth and scales were made of the same tissues found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales. Teeth are among the most distinctive features of mammal species. Paleontologists use teeth to determine their relationships; the shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding.
Carnivores, on the other hand, have canine teeth to tear meat. Mammals, in general, are diphyodont. In humans, the first set starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months can be painful. Kangaroos and manatees are unusual among mammals because they are polyphyodonts. In Aardvarks, teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata. In dogs, the teeth are less than humans to form dental cavities because of the high pH of dog saliva, which prevents enamel from demineralizing. Sometimes called cuspids, these teeth are shaped like points and are used for tearing and grasping food Like human teeth, whale teeth have polyp-like protrusions located on the root surface of the tooth; these polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber.
While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a small layer of enamel at the tip. This small enamel layer is only seen in older whales where the cementum has been worn away to show the underlying enamel; the toothed whale is a suborder of the cetaceans characterized by having teeth. The teeth differ among the species, they may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, a tooth containing millions of sensory pathways and used for sensing during feeding and mating, it is the most neurologically complex tooth known. Beaked whales are toothless, with only bizarre teeth found in males; these teeth may be used for feeding but for demonstrating aggression and showmanship. In humans there are 20 primary teeth, 28 to 32 of what's known as permanent teeth, in addition to other four being third molars or wisdom teeth, each of which may or may not g
Fishing bait is any substance used to attract and catch fish, e.g. on the end of a fishing hook, or inside a fish trap. Traditionally, nightcrawlers and smaller bait fish have been used for this purpose. Fishermen have begun using plastic bait and more electronic lures, to attract fish. Studies show that natural baits like croaker and shrimp are more recognized by the fish and are more accepted. Which of the various techniques a fisher may choose is dictated by the target species and by its habitat. Bait can be separated into two main categories: natural baits. Using lures is a popular method for catching predatory fish. Lures are artificial baits designed to resemble the appearance and movement of prey small fish; the lure may require a specialised presentation to impart an enticing action as, for example, in fly fishing. A common way to fish a soft plastic worm is the Texas rig; the natural bait angler, with few exceptions, will use a common prey species of the fish as an attractant. The natural bait used may be dead.
Common natural baits include worms, minnows, frogs and insects. Natural baits are effective due to the lifelike texture and colour of the bait presented. Cheese has been known to be a successful bait due to its strong smell and light colours; the common earthworm is a universal bait for fresh water angling. Grubs and maggots are excellent bait when trout fishing. Grasshoppers and ants are used as bait for trout in their season, although many anglers believe that trout or salmon and many other fresh water fish roe is superior to any other bait. In lakes in southern climates such as Florida, United States, fish such as bream will take bread bait. Bread bait is a small amount of bread moistened by saliva, balled up to a small size, bite size to a small fish. Most common earthworm species, such as Lumbricus terrestris, which can be dug up in the garden, are eminently suitable for freshwater fishing. However, on a commercial scale they are not candidates for worm farming for providing fishing bait; the greyish brown common earthworms are deep burrowing and do not breed in the shallow worm farm bins.
The red compost worms, such as the well known red wiggler or the European nightcrawler, are better candidates, as they are epigeic, or surface dwellers. This is the reason that red worms are more available commercially for bait worms, their natural home is just below the surface in dung heaps and other plant litter. They are called detritivourous; the larger species, the European nightcrawler is much sought after for fishing bait as it tolerates near freezing water and is one of the few earthworms suitable for salt-water fishing. These worms can grow up to 7 inches in length, but are between 3 and 4 inches long. Worm farmers offer other worm species for bait, depending on availability, which depends on the prevalent climatic conditions; the capture and culture of bait fish can spread damaging organisms between ecosystems, endangering them. In 2007, several American states enacted regulations designed to slow the spread of fish diseases, including viral hemorrhagic septicemia, by bait fish; because of the risk of transmitting Myxobolus cerebralis and salmon should not be used as bait.
Anglers may increase the possibility of contamination by emptying bait buckets into fishing venues and collecting or using bait improperly. The transportation of fish from one location to another can break the law and cause the introduction of fish alien to the ecosystem. Bait machine Chumming Groundbait Live food Commonly used fishing baits in the United Kingdom