Guppy Fact Sheet
The Guppy, Poecilia reticulata, is an attractive and normally peaceful fish. It was named after Robert John Lechmere Guppy who discovered this fish in Trinidad, and believed that this was a previously undiscovered fish. After being scientifically described, the fish was called Girardinus guppii. The common name of Guppy was given the fish.
The Guppy males tend to have a smaller body and bigger fins than the female. The fin underneath the fish in about the centre of the fish’s body (the anal fin) is long in the male and is used in fertilisation. The male is capable of pointing it forwards so it can make contact with the female and transfer the sperm. In the female, this fin is triangular in shape. The males tend to be much more colourful than the females. Modern female guppies often have bright colours, but the wild ones did not. Modern Guppy males often have purer colours, while the wild ones have more varied ones. Often the wild males have more colours on each fish.
It was later found that the fish had been previously discovered by Wilhelm C. H. Peters, described and named. The fish is now usually called Poecilia reticulata. The most common of the common names is ‘Guppy’. There are several other common names including ‘Rainbow Fish’ and ‘Millions Fish’. The name Rainbow Fish is appropriate to its many and varied colours, but is misleading because of the several other fish with the same name. I prefer the name “Guppy". However, the name ‘Guppy’ is sometimes used for other fish. Fish I have seen called ‘Guppies’ include goldfish, Neon Tetras, Zebra Danios and Gambusia. This is misleading and can be confusing.
Guppies are native to several Caribbean islands and north western South America including Barbados, Guyana, Netherlands Antilles, Trinidad and Tobago, the US Virgin Islands, Venezuela and Brazil.
The Guppy is a popular aquarium fish, and can be kept with other small peaceful fish, including Platies, Swordtails and Mollies. It is in the same family as these fish and is in the same genus as Mollies. Other fish suitable as companions are White Cloud Mountain Minnows, Neon Tetras, Cardinal Tetras, Siamese Fighting Fish, Peppered Catfish and other Corydoras catfish, Cherry Barbs, and other small peaceful fish.
Many of the fish just named are schooling fish. I recommend that these be kept in groups of at least four, and preferably more. The Guppy is not a very strongly schooling species and can be kept singly or in small groups, although I prefer larger numbers. It is both the way they usually occur naturally, and they look good. A tank of the highly coloured Guppies is a beautiful sight. Males and female guppies can be kept together but if they are I suggest that at least one female be kept for each male. If you keep several males with one female, all the males want to mate with the female and do not give her much peace.
Fish I would not recommend as companions for guppies include Black Widow Tetras, Serpae Tetras, Buenos Aires Tetras, Paraguay Tetras, Red Eye Tetras, Tiger Barbs, Rosy Barbs, Paradise Fish, Galaxias, and any other fish that can be fin nippers. Larger fish are also generally not suitable companions for Guppies.
The Guppy is easy to feed. They are omnivores like most fish, and benefit from some vegetable food including algae. Guppies will eat most fish food. I suggest a good flake food as a basis for the diet, if possible supplemented with other food to give variety. Good flakes include the Wardley Total Tropical or Total Colour. As well as Wardley there are many other reputable manufacturers of fish food who make excellent foods. Other foods can include live food like Daphnia. Mosquito larvae (Wrigglers) are an excellent food. In the wild, Guppies will eat a lot of these. Their upturned mouth is well adapted to eating wrigglers. Blood Worms are related to wrigglers and are also a good food. Frozen Blood Worms are also good, as are several other frozen foods. Live or frozen Brine Shrimp are good. I also find that Guppies will benefit from dry fry food as a change.
Do not overfeed your fish. I suggest feeding once a day, but not too much. For most types of food the fish should have finished it in a couple of minutes. Guppies are good eaters and generally will get the food quickly. Larger food including Algae Wafers is also good. Because these are hard, the Guppy will take longer to eat them.
Guppies generally thrive in fairly hard, slightly alkaline, water. They can tolerate very large amounts of salt in the water. In some countries they are bred in water which is a mixture of half fresh water and half sea water. The Guppies thrive in this water, but these fish can cause problems when people put them into normal fresh water aquariums. As well as having to be acclimatised to the fresh water, the Guppies have not been exposed to columnaris disease. These fish can die very quickly in a normal aquarium unless strong treatment is done quickly. To get immunity the fish have to be exposed to the disease, and the disease cured.
Rain water is not good water for guppies but many people have used it successfully. If this is the water you have, I suggest using a rainwater conditioner (A mixture of salts). If you are using tap water (as I do), make sure you get rid of the Chlorine or Chloramine.
For a tank of mixed small tropicals, I suggest a pH of 7 and a moderate amount of salt and hardness. In most places normal tap water, with the Chlorine or Chloramine removed, and the pH adjusted to 7 is suitable for Guppies, and to a mixed community. If in doubt about your tap water, I suggest visiting your local aquarium store. They should know about the local water.
The Guppy is a tropical fish. However, different strains of Guppy have different tolerances to low temperatures. I have even heard of strains that are claimed to be able to tolerate temperature down to 4̊ C (39̊ F). I have never encountered any of these. Once I heard of a creek to the north of Adelaide that was supposed to have a naturalised strain of Guppies. I searched for the creek. I identified the creek from the description I was given but there were no Guppies in it. (Actually, there was not even any water!) Although I tried to find where the Guppies would have gone, I was unable to find any Guppies. I suspect that this was a case of mistaken identity of the fish.
As a general thing I would not suggest a temperature of lower than 18̊ C (65̊ F). Guppies will tolerate up to at least 32̊ C (90̊F), and probably higher. Although I sometimes give the maximum and minimum temperatures types of fish can tolerate, it needs to be remembered that subjecting fish to their limits is not good and you are stressing the fish very badly. Stress will leave the fish very vulnerable to disease.
I generally set the thermostat at 24̊ C (75̊ F) although some people prefer a few degrees higher, especially for breeding.
The Guppy is probably the easiest fish of all to breed. The only way of being sure that you will not get baby Guppies is to get only male Guppies. Many people do this and the Males are more colourful. Getting only female Guppies is not a reliable way of preventing reproduction because the Females could have mated before you got them. Unlike with most fish, fertilization in Guppies is internal. This also applies to their near relatives, the Mollies, Platies and Swordtails.
A female Guppy can have more than one lot of babies from one mating, so the mating could have happened a considerable time before birth. The gestation period of Guppies averages about 28 days. This varies with external factors. The water temperature may have an effect. Higher temperatures may shorten the gestation period, and day length also seems to be important, with a longer day length shortening the gestation.
A female Guppy can often become pregnant at as young as two months, having her first babies at three months old. She can continue having babies every 28 days or so for the rest of her life. The Guppy produces fewer babies in each litter than most fish, but the babies are bigger in relation to the fish’s adult size than most fish babies. This frequently gives a high survival rate. This coupled with the short generation time means that Guppies can multiply quickly. In some places there are so many Guppies visible in the water that they have been called the ‘Millions Fish’.
Most strains of Guppy eat their own babies, as well as the babies of other fish. Most types of other fish will eat Guppy babies (White Cloud Mountain Minnows might not) so in a community tank the babies have a very dangerous life. Occasionally one or two will survive in a well planted tank with not too many fish.
“Guppy traps’ or similar arrangements are often used to separate the female and save the babies. They are far from perfect. The female may get excessively stressed in the ‘trap’ and may even die from the stress. If you have a separate tank you can often catch some of the babies soon after birth and transfer them. Another way I have used is to have a very well planted tank, and only put one of two female Guppies in. The females can be kept well fed and if they are available, Daphnia can be continuously present. In these conditions, the females are less likely to eat the babies. After giving birth, the mother fish can be removed. The baby fish will eat the baby daphnia and grow well.
Raising Baby Guppies
Baby Guppies can eat normal fish food of small sizes but they do better on a fry food. I greatly prefer the dry fry foods to the liquid ones. To get the best growth out of your babies, some live food is very beneficial. I use Daphnia screened through a coarse aquarium net so only the smaller Daphnia are given the babies, although the larger Daphnia will not harm the baby fish and will breed in the tank.
Newly hatched brine shrimp can also be used, if you can get the eggs.
In some cases interspecific hybrids between Guppies and Mollies occur. It is reported that these hybrids are sometimes fertile, although I have never tested this. If a cross was done and the babies found to be infertile, this does not prove that this will happen every time. Guppy-Molly hybrids are fairly drab in colour.
Hybrids can also occur between Guppies and the Endler’s Livebearer. These are reported to be fertile. Guppy-Endler’s livebearer crosses are colourful. It would be a shame if the Endler’s Livebearer became extinct as a pure species.
The modern Guppies have been selective bred for colour and fin length, as well as other external characteristics. In the process they have lost much of the original hardiness of the Guppy. The life span of the Guppy now is often no more than a year.
The Guppy has been introduced to every continent except Antarctica. In some places it is causing considerable damage to the native fish of the areas it has been introduced to. You should not release aquarium or pond fish into the wild, and you should ensure that they cannot get introduced accidentally.
It is worthy of note that many of the most destructive introduced fish and other animals have been introduced deliberately, often by government agencies.