Breeding Guppies - Anatomy

The Anatomy of a Guppy

The guppy is one of the smaller of the infinitely varied species of the great fish family. It lives in tropical warm water, can stand brackish water, and as we have seen, it is a member of the smaller pike family.

The color of the guppy is due to color spots, microscopic in size, called melanophores, located in the skin. The number and arrangement of these color areas is what gives great variation among all but the most inbred specimens of fancy guppies.

Outwardly, the fish we see takes its form from the supporting skeleton. The vertebral column runs from its head to its tail and is made up of many separate tiny perforated bones called vertebrae. The head at its anterior end contains the brain case or cranium. The upper and lower jaws are formed of bones. Ribs are attached to the vertebrae and protect many of the vital organs just as they do in ourselves. Fins project from the body at various points. There are also a hip or pelvic girdle and a shoulder girdle which help support the fins. A bony plate called an operculum, one on each side, covers the gills.

The dorsal fin of the guppy is often the fish's crowning glory, standing as it does straight up from the ridgepole formed by the backbone, or lying supinely, and often extending, especially in exotic specimens of fancy guppies, past the end of the tail. The pair of triangular fins at the sides are called pectoral fins, the tail is the caudal fin, the fins along the underside of the body are named for their positions. Thus we find the ventral pair called pelvic fins, and the single anal fin which contains double fin rays, joined so closely as to appear single.

Fins are supported by two kinds of fin rays. One is hard and unbranched, the other is soft and branched, with segments. Swimming is accomplished almost entirely by the movement of the fish's tail which propels by making a sort of figure eight. All the other fins help in guiding, elevating and descending. Watch any guppy and you will see he guides himself chiefly in a certain direction simply by turning his body.

The Digestive System
Guppies have teeth in their jaws and in the roof of their mouth as well. In the mouth there is a tongue. Behind the tongue is the pharynx and on each side of it we find gill slits which allow water to pass into the gill chamber. Leading from the pharynx to the voluminous stomach is a short gullet or esophagus. From the stomach the intestine moves food, being digested, in a curved route to the anal opening just in front of the anal fin.

The guppy has a liver which manufactures bile for digestion and a spleen which helps purify the blood. Digestion is rapid, as witnessed by the large amount of food which can be handled by a guppy in a day. 

External Body Parts  - (1) mouth, (2) nostril, (3) eye, (4) lateral line, (5) dorsal fin, (6) caudal fin or tail, (7) gonopodium (modified anal fin (8) ventral fin, (9) pectoral fin, (10) operculum covering gills.

Circulatory System
The heart is quite different from that of the mammal. It has two compartments instead of four, an auricle and a ventricle. Blood is forced from the ventricle, when it contracts, to the gills where it picks up oxygen and gives up carbon dioxide. This aerated blood is carried by a dorsal artery - which divides into smaller and smaller vessels - to all the body. The blood in the capillaries gives off oxygen and picks up carbon dioxide and waste which are eventually carried back to the heart via veins. Besides the veins, other tubes, called lymph vessels, help carry the blood from the capillaries to the heart where it is again pumped to the gills.

Gills which serve as lungs, because of their exposed position, are subject to diseases. Each gill consists of a bony arch which has on its front surface teeth-like structures called gill rakers and, on its rear or posterior surface, gill filaments which are always bathed by a stream of water passing from the mouth out beneath the operculumoperculum.

The AirBladder
A guppy maintains its balance and position in the water by the presence of an air bladder in its body cavity. Many blood vessels line the bladder wall and help maintain the gaseous content, regulating the amount of oxygen so that the air bladder helps to furnish a storage reservoir for air as well as acting as an organ of maintenance of volume to assure the fish's replacing an equal weight of water. Experiments indicate that the gas in the swim bladder contains a higher percentage of carbon dioxide than does normal atmosphere.

When starved for oxygen, guppies may come to the surface, exposing their bodies, leaving only their tails submerged; an act made possible by their swim bladders.

An egg-laying species of fish is called oviparous. One which gives birth to young, as mammals do, is caged viviparous. But one which incubates a lot of eggs within the body of the mother and seemingly gives birth to them, is called ovoviviparous. The ovary is lined with germinal epithelium - tiny cells which divide and give rise to descendants. After further division and development, they become eggs, but not until they have acquired a yolk in the process. Young from such species are incubated within the mother from the food within the egg and not food taken from the mother's uterus via a placenta. The young obtain their oxygen and give off waste gases by the close association of tiny capillaries in walls of the follicles in which they develop, with the veinules (tiny veins) in the mother's reproductive tract.

A short passage conveys the tiny developed embryos, as the young are called, up to the moment of birth, to the urogenital pore whence they seem to uncoil and dart away to the safety of foliage or lie motionless on the sand or gravel of the bottom. Their first movements nearly always carry them downward and they rest for some time before becoming active. In a tank, they stay in small schools away from the larger fishes for many days.

The male guppy has, in common with a few other live bearing fish, a gonopodium. At birth, the anal fin of the male guppy appears much like that of the female guppy. As he grows, the fin becomes gradually modified so that in a resting stage, it appears narrow and somewhat longer than that of the female.

The position of the attachment of the fin to the body is also different in the two sexes, the male fin moving gradually forward day by day as the fish ages.

When completely developed, the nine fin rays are crowded together. On the end of the longest ray, the third, we find a hood with a backward pointing hook. This hood folds over the gonopodium. There is no hollow tube in the gonopodium as so many erroneously believe.

The gonopodium is located just behind the urogenital pore. In front of that pore are two pelvic fins, quite different from those in the female. Fertilization is accomplished by the three modified fins all swinging forward together and possibly touching momentarily, thus making a temporary tube through which the male hereditary elements are transmitted to the female guppy.

In the male, the organs in which the germ plasm is stored and in which the spermatozoa are manufactured are called spermaries (in the mammal they are called testes or testicles). A short passage connects the spermaries with the urogenital opening. Spermatogenesis, as the maturing of the sperm from the germ plasm is called, differs somewhat from the process in mammals. The spermaries are filled with tissue composed of basic germ plasm cells (primordial sex cells). All the time, by the process of division, these cells are producing more of their kind. It was once thought that these cells . wear out because of exhaustion, but transplantation experiments in mammals indicate that the germ plasm is immortal and only seems to wear out because the fish or animal who is their custodian ages.

The first cells produced by the primordial sex cells are called spermocytes. These change again into cells with tails which propel them and are called spermatozoa or sperm for short, and lie packed together in cell spaces called spermatocysts. In mammals the sperm lie in tubules with heads toward the outside and tails in. They move along the vas deferens, as the tube is called, in a mass. But in male guppies, they stay in groups encased within a globe called a spermatophore. Not masses of loose sperm, as in the case of mammals, but a line of spermatophores move along the sperm duct to the area closest to the outside, called the emmectory.

As we have already observed, the doubled anal fin of the male guppy is modified to be capable of forward movement and to form a transmission tube when in this position. So far as anyone has been able to tell by careful observation and microscopic study, this tube never enters the body of the female but simply acts as a guide like a gun barrel for directing of the sperm. No one has ever seen the male gonopodium actually enter or even press against the female's genital pore, but the whole action of the mechanical part of the transferal of the sperm is done so rapidly that no human eye can witness it. The magician who fools us by rapid manipulation of cards is slow as molasses compared with the movements of the male guppy. And so it may be that rapid motion pictures will one day reveal the actual mechanics to us. On the basis of what we now know, it appears that the spermatophores are popped into the female's genital pore and once inside are moved into the oviduct.

The female guppy manufactures eggs or ova. The tube which receives the spermatophores of the male and conducts them to the ovary is called the oviduct, when actually it is no such thing, for oviduct means egg duct and the guppy does not lay eggs.

In the oviduct the sperm are released from the membrane which holds them together. Secretions from the female are thought to weaken the membrane and allow the sperm to escape. They move into folds of the organ and wait for eggs to be formed.

The formation of the egg is not unlike that of the sperm. Some of the primordial cells divide, their progeny divide and form eggs. The number of eggs formed is the deciding factor in the number of offspring spawned; there are thousands of sperm for every single egg. Nature is frugal with eggs and extremely lavish with sperm. In one ejaculation from most male mammals there are ten million or more sperm, but in the case of guppies, we do not know how many are received by the female. The number must be very large because one insemination is capable of producing litter after litter for several months-perhaps as many as eight. And in mammals the sperm live but a few days in the reproductive tract of the female.

One of the most remarkable facts about the female guppy is her ability to hold so many of her young, both before and after they are born. Before - even being as distended as she appears, how can seventy-five babies, let us say, be packed away along with their embryonal envelopes in so small a place? And even as interesting is the question of how she can bold so many in her stomach. I have known a female guppy to eat all of her young, just as rapidly as she gave birth to them. Part of this is fear and part protection of the young. If a female is having young quietly - has a swarm around her - and she is disturbed, the young will be missing shortly afterwards. But the reason for eating the young is principally the hunger of the mother.

A most important problem which I have studied is that of determining whether a female guppy, once fertilized, can be fertilized by a second or third male. This experiment was done by mating a gold female to a gold male. While she was giving birth to her golden young, several young natural-colored males were placed in the tank. In her next litter there were no golds; the sperm of the natural-colored males had done the fertilizing. The same experiment was repeated many times with identical results. Then it was tried with albino females with again the same results.

The conclusion seems to indicate that if a female is bred to one male, he can provide sperm for several litters. But, if at about the time of giving birth, the female is mated to another male, the fresher sperm are more likely to fertilize the next batch of eggs. This has practical value in breeding.

The gestation period - the time between fertilization and birth-is 22-24 days. Broods are produced, under optimum conditions, every 27-30 days. The-five or six days difference is accounted for by the time necessary for the development of the eggs to a fertilizable condition.

Fertilization is a most interesting phenomenon in guppies. The sperm enter the ovary where they wait for the ripening of the first batch of eggs. Another crop of eggs does not mature to the point of union with the waiting sperm until the last lot has left the body of the fish as live fry. After birth has taken place, the new eggs develop rapidly and are fertilized by waiting sperm. One report indicates that sperm can wait, dormant in the female's body, for eight months, and still be able to fertilize.

At the age of 30-35 days the sexes can be distinguished by the development of larger body of the female and her 'gravid spot' which males do not show. The male begins to show the developing gonopodium. The distinctive color markings or black spots begin to develop where they can be seen at about the fortieth day onward. Tail colors show, as early as twenty-eight days in the fast grown specimen. Great strain differences exist in this regard, some strains maturing two weeks earlier than others. Rapidly grown males have been known to have the start of color development by twenty-eight days of age. The characteristic black, red and yellow pigments appear to depend upon hormones produced in the testes and this is important to realize. The female hormones repress the colors which the males show. Females subjected to male hormones develop male characteristics. Immature females may receive sperm of mature males and carry it until they are mature. Therefore it is essential to remove all the adult males from a tank of fry, or remove the fry to another tank soon after birth.

The virgin female guppy has a period, once every 4-6 days, when she will accept the male. This fact has been ascertained by watching many and noting that each one, when the temperature was about 80 degrees F, assumed an oblique position in the water. In cold water she seldom, if ever, changes her position although males continue to pursue her even though there may have been no outwardly observable sexual rhythm or possibly no inward changes either. All available evidence tells us that guppies are more prolific in warm tropical water.

There is evidence that the male may produce a substance which, a day after he is introduced into- a tank, will tend to make a female assume the oblique position even in water colder than 80 degrees F. Some breeders contend that they have better results with shy breeding females when they use a large number of males for one female. Possibly it is because of this unknown male-produced substance that is then more abundant that such females tend to become fecund.

Nervous System
Guppies have all the ordinary senses and possibly others not possessed by mammals. The brain is the main organ of perception; a spinal cord of nerves runs through the vertebrae. Guppies smell through nervous connections of the brain via olfactory tracts not connected with the respiratory system; they hear through two closed cavities on opposite sides of the head containing ear stones (otoliths) which convey sound vibrations; they feel through nerve connections in the skin and lateral line organs, unique in fishes; they taste their food; they balance, possibly by their otoliths.

Guppies have furnished worthwhile evidence to neurologists in nerve regeneration. It is possible to cut through the whole spinal cord and have it regenerate in a short time - in some as early as the third day following the operation.

Excretory System Kidneys filter blood and remove waste which is carried to the bladder by ureters. Both kidney and bladder are small organs. The bladder discharges through the urogenital pore, just behind the anus.The gonopodium is located just behind the urogenital pore. Blood carries waste gases to the gills where they are given off into the water.

The Vent:
The vent is situated just in front of the anal fin and waste products of food are excreted here. In the same area is the 'cloaca' which is the urinary and genital duct.

Information Source - "All About Guppies" by Leon F. Whitney, D.V.M.