Order Cyprinodontiformes ( Cyprinodontiformes )
Suborder Cyprinodontoidei ( Cyprinodontoidei )
Family Poeciliidae ( Poeciliidae )
Subfamily Poeciliinae ( Poeciliinae )
Genus Girardinus — Girardinus.
The native home of these small fish is South America. They are found in small flowing water bodies of Cuba, Costa Rica, Argentina, Paraguay, Uruguay, and Brazil. The body is elongated, compressed laterally, especially in the posterior part of the trunk. In males, the anal fin is transformed into an organ of copulation — the gonopodium, and is hook-shaped. These fish resemble simple guppies; their general coloration background is light gray or greenish-yellow, with irregular black spots scattered across the body, though such spots are absent only on the lower belly. The female is larger than the male.
Peaceful, calm fish that can be kept together with other peaceful species. These fish are much less demanding than other livebearers. The aquarium should contain plants, including floating ones. Diet: live and dry food, with a preference for plant supplements. The water can be slightly salted using common salt (2 g per 1 liter of water).
It is best to keep them in an unheated aquarium at a water temperature of 18-20°C. These are livebearing fish. Eggs are fertilized inside the female’s body, and fully formed fry are born, which immediately begin to feed. Spawning takes place in the general aquarium. Pregnancy lasts about 3 weeks.
— Goldbelly Topminnow — Girardinus falcatus [Eigenmann, 1903]. Synonym: Glaridichthys atherinoides, falcatus. (Eng. Goldbelly Topminnow). Cuba. Male 4 cm, female 7 cm. Turquoise, shimmering eyes. Light golden, greenish-yellow coloration, darker in the belly area. Males have an unusually long gonopodium, reaching almost to the base of the tail. Fins are semi-transparent with yellowish shades. This is a peaceful, calm fish that stays near the surface.
Peaceful fish that can be kept with other peaceful species. An aquarium with plenty of fine-leaved plants and floating plants to create sheltered areas for the fry is recommended. Good filtration and regular water changes are required. Omnivorous fish, fed a wide variety of live, frozen, and dry foods. Part of the diet should be plant-based. The number of fry, depending on the size of the female, can range from 25 to 60; they grow relatively slowly. They live up to 3 years. pH 6.5-7.5; dH up to 20°; T 24-28°C.
— Black Metallic Livebearer — Girardinus metallicus [Poey, 1854]. Synonyms: Girardinus garmani, pygmaeus. (Eng. Black Metallic Livebearer, Metallic Topminnow). Costa Rica, Cuba. Male 4 cm, female 7 cm. The body shape of these fish is elongated, laterally compressed. Mouth is superior. The main body coloration ranges from yellow-brown to gray-green, with a metallic sheen of green or blue shade. The belly is light, almost white. Dark and silvery transverse stripes run one after another along the flanks. Sometimes they have a few black spots on the back of the head and the dorsal fin.
The dark edging of the scales forms a reticulated pattern on the body. Several shiny green dots are present below the eye and on the gill cover. Fins are transparent, with a distinct, regularly shaped black dot on the dorsal fin, which is brighter in females. In the male, the snout, belly, and gonopodium are black, and the fins are yellow with a black border. Many males have a black stripe running from the gonopodium to the snout. The female is grayish-silver with a metallic sheen. A selective breeding form is known, featuring an olive coloration with shiny bluish strokes along the body.
Peaceful and very active fish. They can be kept in groups of 8-10 fish in a general aquarium with peaceful neighbors of similar temperament, with patches of thickets and floating plants. They do not form a school, but scatter throughout the aquarium. Keep at least 3 females per male. The water should have a neutral to slightly alkaline reaction; hardness does not play a major role. These fish do not tolerate high water temperatures. It is best to keep them in an unheated aquarium at a water temperature of 18-22°C. They prefer dim light much more than bright sunlight.
Ideal food includes Cyclops, Moina, Artemia, as well as dry foods. Girardinus should not be fed whole bloodworms. The throat of small males is very narrow, and they can choke on whole bloodworms. Feeding tubifex worms causes tuberculosis followed by mass mortality. Common salt (up to 5 grams per liter) and methylene blue (0.1-1 milligram per liter) provide an excellent therapeutic effect for ailments. They mature at 4-5 months, and sexual dimorphism appears at two months of age. After 24-35 days, the female gives birth to 15-40 fry measuring 9 mm. dH 10-20°; pH 6.5-8.0.
Heterandria bimaculata, Heterandria formosa.
Gambusia affinis, holbrooki, nicaraguensis, puncticulata, sexradiata. 
