Goodeids belong to the real (true viviparous) livebearers. Unlike most embryos of poeciliids, goodeid embryos hatch out of the egg within the ovarian follicle. For most poeciliids will develop in an egg and when time of birth enters, the membrane of the egg will break and the newborn will be dropped out of the female's body. To the eye it seems that they are born the way mammals do. 
When goodeids are born, the fry tend to be larger than with most poeciliids. They're a mini copy of their parents and have trophotaneniae (some kind of a ribbon-like structure) at their bellies to nurture themselves for the first 1-2 days. These trophotaneniae will be shed by the fry themselves.
Another difference with most poeciliids is that the males don't have a gonopodium but an andropodium. The andropodium is a notch on the front of the anal fin. The picture below shows the andropodium.

And unlike most poeciliids, each pregnancy should be engaged by a new copulation. Most poeciliid females can store sperm which enables one copulation to accomplish multiple pregnancies. But goodeid females can't...

The larger part of all Goodeids are endemic to shallow waters (fresh and brackish water) in Mexico and some in The United States. Depending on the strain, these livebearers can withstand low temperatures pretty well. Another note that someone should take nortice when starting to keep goodeids is that most of them aren't really adaptable to a community tank. The majority of these goodeids can be dominant in their behaviour and most of them are real fin nippers. They won't nip fins of other goodeids what I've noticed out of experience. Best is to keep most goodeids in a species tank.

With all goodeids I'm keeping and have kept, I've noticed that they do well in an enviroment with a still water surface.

Ameca Splendens

This species is also called butterfly splitfin. The species is endemic to Jalisco in Mexico. A beautiful marmored fish but not suitable for a community tank. They tend to be aggressive to other tank members and real fin nippers indeed. or keep them in a larger sized tank with other breeds of well-sized fish which have a certain dominance in their genes as well.
They're also good algae eaters. It's a diet which they do appreciate. So, in case a lot of algae growth is at hand, these are the fish to keep.
Goodeids in general can be kept outside during spring and fall season. They're easy breeders ( 5 till 20 fry each drop) but it's also a fact that they will reproduce themselves outdoors far more easier than when they're kept indoors.

It's a hardy fish and they'll do also well in a less clean kept enviroment. A male wil reach up to approx. 8cm and a female up to approx. 12cm. A suitable temperature rate can be kept moderate between 20°C -  25°C.

But despite of the fact that the ameca splendens likes temps above 20°C, they can withstand much lower temps as well for they are inhabitant to colder endemic regions in Mexico. I've even harvested them from my outdoor tank during fall at rates of 8°C watertemperature at day.

Xenotoca eisini, San Marcos

Note: This species is called "Xenotoca doadrioi" ever since the year 2016. But I'm using the old scientific name which I'm used to all these years.
This species is also known as the red tailed goodeid and as the red tail splitfin.
A livebearer mainly found in Mexico and to be kept at rates of 18°C - 27°C watertemperature.. With its size one of the moderate sized livebearers. Male will reach 6,5cm and females 7,5cm in length.
 (♀) left, (♂) right
These fish are (as all members of the goodeidane genus) considered being the real livebearers unlike most poeciliids we know. The size of the newborn fry can differ a bit. despite of the fact that they can be large ofspring, their size can be reduced if a batch is large. For most of the time they will drop between 10 - 20 fry.
Above: Ameca splendens & xenotoca eisini, San Marcos.

This livebearer is considered being aggressive and should be kept in a species tank. For also this is a real fin nipper... I've kept these guys in one of the outdoor tanks and they did really well during springtime till fall. Also the reproduction outdoors is phenomenal.
 (♀) top, (♂) bottom

Zoögoneticus tequila

This goodeid is also called "Tequila splitfin" and "Picote tequila". 
This species is to be found in Rio Teuchitlán of the Rio Ameca drainage from the Pacific Slope in Jalisco, Mexico.

It's one of the more impressive goodeids there are to me. There's a difference in coloration between both genders. The male is dark olivaceous on both sides with some greenish and blue 0n both sides. a reasonable 
number of scales are reflective, iridescent as a result. The caudal fin has a broad redish till orange band. The females however, seem more pale in comparison to the male. And mostly with somewhat larger females, a broad band of light orange appears as well in the caudal fin as the pictures below show.

A gestation of this breed will take about 7 - 9 weeks before an average brood of 10 - 15 fry will be born. They'll size up to approx. 6 - 8cm. 
Is this a suitable fish for a community tank? Well, that really depends on the nature of each individual fish. They can be very peaceful but they can be very territorial as well. And they don't always harmonize with other goodeid breeds as well. 

Ilyodon xantusi

A more slender goodeid is the Ilyodon xantusi also known as "Limones splitfin".
This mexican livebearer is to be found in the Rio Colima, Haciendo Los Limones, 2 km southwest of Villa Alvarez.
It's an easy to keep goodeid strain. What's so typical about the reproduction is that the number of fry with each batch does differ a lot with same sized females. So wether that's 10 or 40 fry each batch is hard to predict. Despite of the fact that also fry of this kind are large in size at birth, fry will be less large sized when the number of fry is large. They also leave their offspring at peace. So, hardly fry will be eaten by the adults.

There are specimens which have yellow edged fins but also specimens with more translucent fins with a speckled pattern on them. The speckled pattern on mostly the lower part of the body are leopard-like spots. 

They do well in a wide range of water temperature. Even muddy water doesn't seem to harm them. A good option is to keep this strain outdoors during spring till mid fall where they cabn size up to a decent size.

Ataeniobius toweri

The Ataeniobius toweri also known as "Striped goodeid" or even "Bluetail goodea" is a very slender goodeid.
This strain is endemic to Laguna Media Luna, a drainage of the Rio Verde in Mexico. 

Also this goodeid doesn't really have the obnoxious characteristic of fin nipping which makes this kind suitable in a community tank. It will grow up midsized (approx. 5-6 cm). Males tend to develop a blue shimmer on their fins.

Young fish do show 1-3 stripes on the side which seems to dissappear when hitting adulthood. But when light hits the sides of the fish, you definitely will still see those stripes. Young fish also look more gray-bluish of color.
Unlike most goodeids this strain does prefer higher temperatures. But I do have to admit that they do well as well at lower rates. I myself keep them at approximately 18-22°C. So, despite of their endemic location where it's warmer than where most goodeids are to be found, they do adapt quite easily to lower rates. 
Well, it's just a personal preference wether one would call this an interesting fish to keep. It doesn't show too much brightness in color but to me it's the fish itself that interests me. They're more vivid when kept in a group. But a small number of these fish will do fine as well in a tank. So, no pressure to purchase a whole bunch of them.

Characodon lateralis

This goodeid is also known as "Rainbow characodon".
It inhabits a series of small localities below the waterfall (El Saltito) in the upper Rio Mezquital basin,Durango state, central Mexico. And the localities where they are to be found are Los Berros, La Constancia, Amado Nervo, San Juan and last but not least Nombre de Díos.
I myself am keeping fish of Ojo de Agua Los Berros (2005).

The breed I've got are olive-brown bodies and males tend to have more coloration than females do. Both genders have a lateral stripe on both sides (plural blotches on a row) which hardly reaches the caudal peduncle. On the belly they're white till gray. The Los Berros ch.lateralis do show some red in their fins when they've reached adulthood.

Also this breed has got a long gestation with an average of 7- 9 weeks and afterwards an average number of 5 - 20 fry will be born.

They tend to grow slowly and they'll size up to 4 - 6cm.
Despite of the fact that this strain is considered being territorial, I do keep them together with endlers. Which seems to be a good combination.

Neotoca bilineata

This goodeid is also known as "Twoline skiffia" and "Tiro de dos rayas".
This species originates from the Pacific Slopes and inhabits the Rios Lerma-Grande de Santiago basin and the endorheic Rio Grande de Morelia basin in the States of Jalisco, Michoacán and Guanajuato.

They prefer slow running water. Furthermore, they're really adaptable to a wide range of temperatures. The only problem that occurs when held at higher temps is that they won't outgrow that much. Reproduction at higher and lower temps doesn't seem to be of any influence. Even at rates of 8°C - 12°C won't stop them from breeding.
Above: An adult male                                                                Above: An adult female

Both genders are almost equilly cloured. But an adult male will develop a dark coloured dorsal fin and anal fin. The caudal fin however won't get so dark.

Above: An adult pair. Clearly a pregnant female...
After a gestation of approx. 4 - 5 weeks a number of 10 - 20 fry will be born. They'll size up to max. 3 - 5cm. 
Furthermore, it's a more peaceful goodeid and can be kept together with other peaceful fish.

Girardinichthys  vivipares 

Another smaller goodeid which seems very peaceful is the Girardinichthys vivipares also known as Chapultepec splitfin. 
This small goodeid is mainly to be found in almost still and shallow waters of the endorheic basin of Valle de México (Valley of Mexico). According to literature this species was also found in other areas (by natural influences or by man seems not clear).

They color will range from grayish till a bit sand colored and somewhat speckled pattern on the scales. Also the edges of the fins is a bit darkened. Males tend to have a bit darker coloration in comparison to females. And during courtship males can become darker for that matter. 
But also dominant males can become very dark till real black. A good examle is shown in the following two pictures below.

The male in the front is a dominant (alpha) male and the male in the back shows a beta male. But the beta male does show ferm dark edges on its fins. On the next pictures a juvenile male is shown which is getting his fins dark edged.
To keep them well they need to be kept at lower temperatures. Long term higher temperature exposing won't do them any good. For they will live much shorter than the expexted lifespan. They do also well in muddy till very clear water. So, that's a lucky break for someone who's lacking a good maintenance quality. But I'm not encouraging low maintenance with these fish by any means to be honest. In some way, it also takes a bit longer before this strain comes to adulthood. 
Below: An adult female.

This is such a friendly goodeid which doesn't nip at other fish's fins. It's very suitable to be kept with other friendly fish which can be kept at lower temperatures. In case you wonder what their favorite food might be... it's algae! 

Above: An adult couple Girardinichthys vivipares.

Soon on this page:
Chapalichthys pardalis
Allodontichthys tamazulae
Alloophorus robustus
Zoögeneticus purhepechus
Skiffia multipunctata