What is a wild-type guppy? That can be a complicated question, as will soon be apparent. However, we do have to work with some kind of definition. To put it concisely, a wild-type guppy is a guppy that has a phenotype (its observable physical characteristics) that is consistent with the appearance of guppies in the wild. This is a broad definition, because wild guppies are incredibly diverse in color, color pattern, and fin shape. It is from this diversity that the fancy strains have been developed. When people talk about phenotype, there is another side to the coin, which is the genotype (the genes or alleles an animal carries, many of which may not be expressed). Some people might argue that a guppy with a wild type appearance, but with a rather unique genotype, may not be a "true" wild type. The argument is a bit esoteric, but it can be very important to breeders or people investigating guppy genetics. Wild-type guppies can be divided into four categories, which will be discussed below.
True Wild Guppies
"True" wild guppies are fish taken directly from the wild. Only people with close connections to collectors have access to these fish, or people who live in a region that supports wild populations of guppies. These fish can much variability of characteristics, which will be idiosyncratic to their collection location (the population they come from). Also of importance is their environment. A great deal of research has demonstrated that guppies in low predation areas develop more vibrant coloration, since selective pressure due to sexual selection is more important in these areas than selective pressure by predators that can spot and eat brightly colored fish.
Wild Descended Guppies
Guppies of direct (recent) wild descent can be found at online auction sites, and sometimes, if one is lucky, by trade through aquarist societies. Buying these fish can be expensive, and if ordering them online the cost of shipping will double the price. The high price is partly due to the perceived uniqueness of these fish, but also because there is sometimes demand for these fish by large breeders who are always on the lookout for fresh stock for out crossing, or new mutations for the next award winning strain. Despite the high cost to hobbyists, what these fish have going for them is that they can have very diverse phenotypes. Some caution is necessary, because this isn't always the case. In addition, it may only be relevant if a large number of them are purchased. The hows and whys of this are addressed on Maintenance page.
The very fact that feeder guppies are listed here may seem controversial or bewildering to some. The general opinion expressed on various guppy message boards is that the gene pool of feeder guppies is "polluted" by fancy guppy culls. Occasionally pet stores throw fancy guppy fry or less attractive fish in with feeders. However, most of the time, feeder guppies are ordered from a distributor who gets them from a fish farm. Feeder guppies are typically descended from fancy guppy culls from the commercial breeder...but the feeders may be many, many generations removed from fancy guppies. They were likely tossed in an outdoor pond at some point years ago and let breed at random. They "revert to type," meaning their genes are distributed or sorted back to a more "wild" state. Feeder guppies often sell for as low as 10 for a dollar. This makes them very economical for starting up a wild-type colony of guppies.
A top sword "feeder" guppy.
Arguments against using feeder guppies for this purpose include the perception that they are not as colorful or healthy as "wild descended" guppies. There are a few reasons for this that don't necessarily have anything to do with their genotypes. It is true that after many generations, some feeder guppy gene pools may lose genes for varied and vivid color, but this can be true of any colony of wild-type guppies over time. There will be more on this later. More pressing concerns to feeder guppies have to do with their living conditions and nutrition.
Feeder guppies are often raised in huge outdoor ponds, where they are overcrowded and malnourished. In these conditions, disease runs rampant. Thus, when they reach pet store tanks they are drab, diseased, and stunted. Many of the fish will not live. They behave in a dysfunctional way because of their crowded conditions, and can be very aggressive, skittish, and territorial. However, there can be diamonds in the rough, so to speak, and proper water conditions and good nutrition will be required before one can properly assess whether the fish have attractive phenotypes. It might even take another generation of proper conditions if the fish are terribly stunted. This requires patience, but for the hobbyist on a budget it can be a fun adventure.
Endler's Livebearers (Cumana' Guppy)
Endlers livebearers are probably becoming the most popular wild-type guppies, but when purchasing them one faces the same cost burden as other wild descended guppies. There is a long and controversial history surrounding Endlers, which is best left to a google search. However, some things should be said as they are relevant to discussion here. Many aquarists are firmly against hybridizing fish, especially when the fish are endangered. It really is yet to be seen whether Endlers are endangered, or whether they are even truly of different species from guppies (evidence suggests they may be behaviorally different and possibly phenotypically different, but not genetically different). Nonetheless, if one breeds these to guppies, full disclosure of this fact is the only ethical path when trading or selling hybrids. Strict records should be kept to ensure that one knows, to the best of one's ability, the pedigree of the fish kept. If there is ever a consensus that Endlers are simply from another population of wild guppies, then this concern can be discarded. Having said all of that, professional breeders have already used Endlers as outcrosses or to help develop new strains of fancy guppies, so in some sense the cat is out of the bag. It is likely that soon many of today's top quality fancy strains will have Endler blood, if they don't already.