Guppies are a small, pretty species of fish that are extremely popular for home aquariums. While they’re fun in captivity, in the wild they can cause major trouble. Native to South America, guppies are an invasive species on nearly every other continent and, as a result, have led to declining native fish populations.
What Are Guppies?
Guppies (Poecilia reticulata) are a species of small tropical freshwater fish that are common in aquariums.
Guppies are sexually dimorphic, meaning there are distinct differences between males and females of the species. Male guppies are brightly colored in shades of black, green, orange, red, white, and yellow and have patterns like speckles, spots, and stripes. Females are a solid silver color. Guppy size also depends on the sex: males range in size from just under an inch to 1.4 inches (25 to 35 millimeters), while the females are larger, 1.5 to 2.4 inches (40 to 60 millimeters).
Because they’re so populous, they’re also often used in genetic research.
Guppy Habitat and Invasiveness
Guppies are native to certain countries and islands in South America: Antigua and Barbuda, Barbados, Brazil, Guyana, Suriname, Trinidad and Tobago, and Venezuela. They live in either freshwater or brackish water, which refers to areas where salt and freshwater meet, but their habitats can range greatly. While typically found in freshwater streams, they may live in estuaries, irrigation channels, lagoons, lakes, ponds, and reservoirs in many elevations.
Often the only species found in heavily polluted bodies of water, guppies can withstand a wide range of water environments. They tolerate water ranging from 64.4 to 82.4°F (18 to 28°C) and salinity of up to 150% seawater. They prefer the water to be slightly alkaline, with a pH of 7.0 to 8.0.
Because they adapt so well, guppies have made their way to countries on every continent except Antarctica. In some cases, they were released on purpose to help control mosquito populations, but in general did not affect mosquito populations at all. Instead, they’ve harmed the local ecologies, as they will eat native insects and the eggs of native species of fish.
In the U.S., guppies have been found in many states, most likely the result of aquarium or fish farm releases:
- New Mexico
- New York
- West Virginia
Guppies have also been found in the territories of Puerto Rico, the Virgin Islands, and Guam. They are considered a now-established species in Hawaii, Idaho, New Mexico, Nevada, Texas, and Wyoming. So far, they’ve been implicated in the decline of several subspecies of White River springfish in Nevada, the Utah Sucker in Wyoming, and damselflies in Oahu, Hawai’i.
Guppies are also dangerous as an invasive species because they carry several diseases and parasites that can similarly damage local populations. Parasites and nematodes include:
- Bothriocephalus acheilognathi
- Camallanus cotti
- Contracaecum rudolphii
- Gyrodactylus bullatarudis
- Gyrodactylus turnbulli
- Ichthyophthirius multifiliis
- Tetrahymena corlissi
Viruses can include epizootic hematopoietic necrosis virus, a disease that causes the death of kidney tissues, the liver, and the spleen, as well as European catfish virus and European sheatfish virus, which can cause lesions on and death of internal tissues and organs.
What Do Guppies Eat?
Guppies mainly eat algae, invertebrates like insects, and debris from the water. Unfortunately, they’ve also been found to prey on the eggs and larvae of other fish species, often causing population declines.
Guppy Lifespan and Life Cycle
Guppies don’t live very long in the wild, an average of two years. Many things can influence this, though, including their location and what predators are nearby.
Male guppies reach sexual maturity at two months old, while female guppies reach sexual maturity at three months old. Males are extremely sexually aggressive, and if females reject their advances, the males may try to forcefully inseminate them. This often doesn’t work very well, since the females can eject this sperm before fertilization happens.
Female guppies can also store sperm for up to eight months inside their bodies to fertilize eggs at will. They don’t lay eggs but instead give birth to live young after four to six weeks. Depending on the female guppy’s age and the number of predators around, her litter size can range from one to 100 offspring, but 20 to 40 is average. Female guppies can give birth two to three times a year, and they can continue to reproduce until they are 20 to 34 months old.
Newborn guppies don’t need parental care, and the adults don’t offer any. Parents may prey on their own young.
Guppies are an extremely popular species of fish for home aquariums. While they’re a small species and not too difficult to care for, there are a few things to keep in mind.
Tanks. Guppies are small, but they’re active and need plenty of space to swim around. A 4-gallon tank is the absolute smallest you should go for a guppy tank. Ideally, your guppies should have at least a 10-gallon tank. Guppies can have decorations in their tank, but keep an eye out for anything that might snag their fins.
Water. Wild guppies prefer pH levels of 7.0 to 8.0, but commercially-bred guppies can handle pH levels between 6.0 and 9.0. They’re also comfortable in temperatures between 70 and 82°F (21.1 and 27.8°C), but their temperature should not drop below 59°F (15°C) or exceed 102°F (39°C), as this will likely lead to death.
While guppies are hardy, you still need to introduce them to their water carefully. The drip acclimation method, in which you slowly introduce aquarium water, works well for guppies.
Diet. Guppies swim near the top of the water, so small, floating pellets and watered-down flakes work well. Some guppies may prefer to look for food lower down, so you may need to experiment with different types of food to find what works best for your guppies.
Tankmates. Guppies usually swim in groups and will likely be happier in a tank with other guppies. There should be at least three guppies together, and if you’re mixing genders, at least 66% should be female. Don’t house guppies with any aggressive species.