Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's frog, fishes are by far the most diverse mouthbrooders. Mouthbrooding has evolved independently in several different families of fish.
Paternal mouthbrooders are species where the male looks after the eggs. Paternal mouthbrooders include the arowana, the mouthbrooding betta Betta pugnax, and sea catfish such as Ariopsis felis. Among cichlids, paternal mouthbrooding is relatively rare, but is found among some of the tilapiines, most notably the black-chin tilapia Sarotherodon melanotheron.
In the case of the maternal mouthbrooders, the female takes the eggs. Maternal mouthbrooders are found among both African and South American cichlids. African examples are the haplochromines, such as the mbuna and the dwarf mouthbrooders Pseudocrenilabrus multicolor, and some of the tilapiines, such as Oreochromis mossambicus and Oreochromis niloticus. The South American maternal mouthbrooders are all members of the Geophaginae subfamily (commonly known as "eartheaters" on account of their substrate-sifting feeding mode) such as Gymnogeophagus balzanii and Geophagus steindachneri.
Biparental mouthbrooding occurs where both parents take some of the eggs. This is relatively rare, but is found among the cichlid genus Xenotilapia, and a single catfish, the spatula-barbled catfish (Phyllonemus typus).
Typically, after courtship, the male fertilises the eggs and then collects them in his mouth, holding onto them until they hatch. During this time he cannot feed. Among the maternal mouthbrooding cichlids, it is quite common (e.g., among the mbuna) for the male to fertilise the eggs only once they are in the female's mouth. Some cichlids are able to feed while mouthbrooding the eggs, but invariably they feed less often than they would otherwise do, and after mouthbrooding one batch of eggs, all mouthbrooding fish will be underweight and requiring a period of time to feed and make good the depletion of their energy reserves.
In all cases, the eggs are protected until they hatch and the fry become free swimming. Only in some cases does the parent extend protection to mobile juveniles. Among the cichlids and arowanas, extension of brood care to the fry is common, and they have behavioural cues to tell fry swimming and feeding away from the parent that danger is approaching and that they should return to their parent's mouth. By caring for their offspring in this way, mouthbrooding fish are able to produce smaller numbers of offspring with a higher chance of survival than species that offer no broodcare.
Some commercially important fish are mouthbrooders, most notably among the tilapiines and arowanas. Fry harvesting, getting the brooding fish to open its mouth and release the fry, is important if the fry are to be reared artificially. In the case of endangered species, such as Asian arowana, harvesting may be supervised by an official who will certify that the fish farm is a genuine producer of captive-bred fish.
Some fish have evolved to exploit the mouthbrooding behaviour of other species. Synodontis multipunctatus, also known as the cuckoo catfish, combines mouthbrooding with the behavior of a brood parasite: it will eat the host mouthbrooder's eggs, while spawning and simultaneously laying and fertilizing its own eggs. The mouthbrooder (typically a cichlid) will incubate the cuckoo catfish young, the catfish eggs hatch earlier than the cichlid's eggs, and eat the as-yet unhatched cichlid eggs before being set free.by the parasite
Families of fish known to include mouthbrooding species include:
Mbuna (pronounced mboo-na) is the common name for a large group of African haplochromine cichlids from Lake Malawi. The name mbuna means "rockfish" in the language of the Tonga people of Malawi. As the name implies, most mbuna are cichlids that live among the piles of rocks and along the rocky shores of Lake Malawi, as opposed to the utaka and other "haps," cichlids that live in the open water or on sandy shores or soft substrates. Some species of Mbuna are highly sexually dimorphic, although many are not. Among biologists, it is believed that all of the cichlid species of Lake Malawi, including Mbuna and non-mbuna such as the Utaka, were descended from one or a very few species that became cut off from each other through periods of decreasing water levels that formed the three Great rift lakes into many smaller lakes. In isolation they adapted to their immediate surroundings. With time the waters again rose, and these new species were forced to adapt, once more, to new competition. The introduction of these, now highly specialized species to each other, created some very strange adaptations and unique behaviors making them some of the most unusual fresh water fish in the world. Their wonderful colors, intriguing behavioral characteristics and relative hardiness make them very popular despite their unique demands for the home aquarist.
These cichlids are some of the most colorful freshwater fish for the home aquarium. Mbuna are very aggressive and territorial fish, they are not suitable for beginner fishkeepers. A suitable aquarium setting includes many rocks, adequate filtration, caves and hiding places; plants may be uprooted so they are best avoided but a small number will work well in the aquarium. One of these is Java fern, which may become the object of mbuna aggression but will not be eaten due to an undesirable taste.
Sand or gravel is the ideal substrate. The hobbyist will want to mix in some sort of so-called "tufa rock" as a pH buffer. However, Limestone, Holey rock, aragonite, crushed coral and especially mixed bags of substrate do. Generally, tanks of no less than 120 centimetres (3.9 ft) in length is required for mature Mbuna; 110 litres (24 imp gal; 29 US gal) tanks will work beautifully for juvenile fish but will need to be upgraded as they mature, grow and become more aggressive and territorial (this will occur in just a matter of weeks or months). Ideally, no smaller than a fifty five gallon tank should be considered as adequate space for a colony of Mbuna. In the wild Mbuna are mostly omnivores; their diet consists of insect larvae and aufwuchs and they generally benefit from a varied diet.
While like any aquarium, the African cichlid tank can be decorated to the aquarist's liking, Mbuna will far more enjoy a tank that is designed including numerous cave or hiding places. These caves are easily formed using rocks as would be found in the Mbuna's natural environment or the aquarist can use artificial means. Some popular options are inexpensive flower pots or prefabricated items from a local pet supply store. The flower pot method involves purchasing clay flower pots of a suitable size and chiseling out one side, such that the pot can be easily planted into the substrate to create a cave. It is recommended that the freshly broken edges be sanded down to avoid harming tank inhabitants, as Mbuna tend to be rowdy. Another less popular option, because of cost, is a three dimensional background. These backgrounds can be extremely costly, although some aquarist construct backgrounds themselves.
Because of Mbuna's ferocious digging habits and the recommended sand/crushed coral substrate under gravel filtration is not recommended. High volume hang over the back (H.O.B.), high capacity power filters or canister filters are recommended. For example, on a fifty-five gallon aquarium will be adequately filtered with the use of two four hundred gallon per hour(G.P.H.) In more advanced setups (75 gallons or more) a refugium maybe be a more effective method for filtration. These cichlids must be kept in well filtered, heavily stocked mbuna-specific aquariums. Small, high flow circulation impellers are utilized to circulate water through crevices and stir up detritus that maybe become deposited within the rock work and caves.
Mbuna exhibit strong social behavior and establish a clearly visible social hierarchy including well defined and enforced territories. A dominate male will maintain a spherical territory only allowing females to enter this territory for breeding purposes. Over-crowding helps spread out the aggression caused by these territorial conflicts. By over crowding, it is possible to break down these barriers and create an environment where no particular individual gets bullied to death. They are maternal mouthbrooders and breed readily in good conditions. Most species thrive in colonies made up of 1M and 3-5F. This allows the gravid females to hide peacefully until gestation by dispersing the males advances throughout the harem.
All species from Lake Malawi thrive in the temperature range of 77-84°F. pH 7.5-8.4 is ideal with an almost pristine (near 0 ppm) Ammonia and Ammonium Nitrite content, Ammonium Nitrate levels are controlled by water changes as needed to maintain these demanding levels. Due to the high mineral content of Lake Malawi many Aquarists supplement their water with specific salts and mineral additives. This mineral content is comprised predominately of sodium, calcium, magnesium and potassium. GH / KH A GH value over 10 is a good starting point (moderately hard water). KH values are not so crucial for the well being of the Malawi cichlid but it can help a lot to keep the pH stable even if something goes wrong (carbon dioxide injection or overfeeding). A KH value of 8-10 is a sure bet.
Many mbuna cichlids are regularly stocked and sold by pet shops. Some of the most common ones are the Bumblebee Cichlid or Hornet (Pseudotropheus crabro), Golden Cichlid (Melanochromis auratus), Electric Yellow or Yellow Lab cichlid (Labidochromis caeruleus), red zebra cichlid (Maylandia estherae), Blue Zebra (Maylandia callainos), and Melanochromis cyaneorhabdos (Blue Johannii) cichlid. Many of these species are considered to have large territorial needs and will aggressively defend these territories making them a handful for the ill-prepared novice hobbyist. Cichlids belonging to any of the genera listed below are considered mbuna.
The list below includes groups of non-mbuna mouthbrooding cichlids from Lake Malawi.
In zoology, an egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg (Latin, ovum) is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing embryo can survive on its own. The term "egg" is used differently outside the animal kingdom, for an egg cell (sometimes called an ovum). Reproductive structures similar to the egg in other kingdoms are termed spores, or (in spermatophytes) seeds.
Oviparous animals are animals that lay eggs, with little or no other development within the mother. The study or collecting of eggs, particularly bird eggs, is called oology.
Reptile eggs, bird eggs, and monotreme eggs, which are laid out of water, are surrounded by a protective shell, either flexible or inflexible. The special membranes that support these eggs are traits of all amniotes, including mammals.
Eggs laid on land or in nests are usually kept within a favourable temperature range (warm) while the embryo grows. When the embryo is adequately developed it breaks out of the egg's shell. This breaking out is known as hatching. Baby animals which have just hatched are hatchlings, though standard names for babies of particular species continue to apply, such as chick for a baby chicken. Some embryos have a temporary egg tooth with which to crack, pip, or break the eggshell or covering.
The 1.5 kg (3.3 lb) ostrich egg is the largest egg currently known, though the extinct Aepyornis and some dinosaurs had larger eggs. The Bee Hummingbird produces the smallest known bird egg, which weighs half of a gram. The eggs laid by some reptiles and most fish can be even smaller, and those of insects and other invertebrates can be much smaller still.
Several major groups of animals typically have readily distinguishable eggs.
Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the Grey Partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigments biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting.
Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors.
However some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid state lubricant. If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.
For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex determining W chromosome (female birds are WZ, males ZZ).
It used to be thought that color was applied to the shell immediately before laying, but this research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral.
In species such as the Common Guillemot, which nest in large groups,each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed.
Bird eggshells are diverse. For example:
Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen's egg has around 7500 pores.
Most bird eggs have an oval shape, with one end rounded (the aerus) and the other more pointed (the taglion). This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointy end develops at the back. Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.
Many animals feed on eggs. For example, principal predators of the Black Oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The stoat (Mustela erminea) and long-tailed weasel (M. frenata) steal ducks' eggs. Snakes of the genera Dasypeltis and Elachistodon specialize in eating eggs.
Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
An average Whooping Crane egg is 102 mm (4.0 in) long and weighs 208 g (7.3 oz)
Eurasian oystercatcher eggs camouflaged in the nest
Egg of a Senegal Parrot, a bird that nests in tree holes, on a 1 cm (0.39 in) grid
Eggs of ostrich, emu, kiwi and chicken
Finch egg next to American dime
Eggs of duck, goose, guineafowl and chicken
Eggs of ostrich, cassowary, chicken, flamingo, pigeon and blackbird
Egg of an emu
The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.
A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.
In certain rare scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.
The eggs of fish and amphibians are jellylike. Cartilagenous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. 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 eggs of the egg-laying mammals (the platypus and the spiny anteaters) are macrolecithal eggs very much like those of reptiles. The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta. The young are born at a very early stage, and can be classified as a "larva" in the biological sense. In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.
Eggs are common among invertebrates, including insects, spiders, mollusks, and crustaceans.
All sexually reproducing life, including both plants and animals, produces gametes. The male gamete cell, sperm, is usually motile whereas the female gamete cell, the ovum, is generally larger and sessile. The male and female gametes combine to produce the zygote cell. In multicellular organisms the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo. In most animals the embryo is the sessile initial stage of the individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote, the sessile organic vessel containing the developing embryo, or even the ova itself may be called the egg.
Like amphibians, amniotes are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals.
Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth").
Dinosaurs laid eggs, some of which have been preserved as petrified fossils.
Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes.
Scientists often classify animal reproduction by degree of development that occurs before the new individuals are expelled from the adult body, and eggs by the degree of yolk they include.
Vertebrate eggs can be classified by the relative amount of yolk. Simple eggs with little yolk are called microlecithal, medium sized eggs with some yolk are called mesolecithal, and large eggs with a large concentrated yolk are called macrolecithal. This classification of eggs is based on the eggs of chordates, though the basic principle extends to the whole animal kingdom.
Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians the dividing eggs develop directly into a simple larva, rather like a morula with cilia. In cnidarians, this stage is called the planula, and either develops directly into the adult animals or forms new adult individuals through a process of budding.
Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods. In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are the norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae, which may be markedly different from the adult animal.
In placental mammals, where the egg is nourished from the mother throughout the whole fetal period, the egg is reduced in size to essentially a naked egg cell (zygote).
Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole.
The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails. Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.
Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryo have enough food to go through a full fetal development in most groups. Really macrolecithal eggs are only found in selected representatives from two groups: Cephalopods and vertebrates.
Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelope it at a later stage. A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs do not allow for direct development, and the eggs hatches to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitate structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo do not suffocate or get poisoned from its own waste while inside the egg, see amniote.
In addition to bony fish and cephalopods, macrolecital eggs are found in cartilaginous fish, reptiles, birds and monotreme mammals. The eggs of the coelacanths can reach a size of 9 cm in diameter, and the young go through full development while in the uterus, living off the copious yolk.
Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous) from live-bearing (Latin. viviparous).
These classifications are divided into more detail according to the development that occurs before the offspring are expelled from the adult's body. Traditionally:
Eggs laid by many different species, including birds, reptiles, amphibians, and fish, have probably been eaten by mankind for millennia. Popular choices for egg consumption are chicken, duck, roe, and caviar, but by a wide margin the egg most often humanly consumed is the chicken egg, typically unfertilized.
According to the Kashrut, that is the set of Jewish dietary laws, kosher food may be consumed according to halakha (Jewish law). Kosher meat and milk (or derivatives) cannot be mixed (Deuteronomy 14:21) or stored together. Eggs are considered pareve (neither meat nor dairy) despite being an animal product and can be mixed with either milk or kosher meat. Mayonnaise, for instance, is usually marked "pareve" despite by definition containing egg.
Many vaccines for infectious diseases are produced in fertile chicken eggs. The basis of this technology was the discovery in 1931 by Alice Miles Woodruff and Ernest William Goodpasture at Vanderbilt University that the rickettsia and viruses that cause a variety of diseases will grow in chicken embryos. This enabled the development of vaccines against influenza, chicken pox, smallpox, yellow fever, typhus, Rocky mountain spotted fever and other diseases.
A baby tortoise emerges from its egg.
Insect eggs, in this case those of the Emperor Gum Moth, are often laid on the underside of leaves.
Fish eggs, such as these herring eggs are often transparent and fertilized after laying.
Skates and some sharks have a uniquely shaped egg case called a mermaid's purse.