Order Characiformes
Family Characidae
Subfamily Aphyocharacinae
Genus Aphyocharax
These are small, slender fishes with streamlined bodies, inhabiting open water columns. In reflected light, they appear silvery with various shades. The fin bases of many species are red. The male is more slender and smaller than the female, bearing a hook used to attach to the female during spawning. When netting a male, it may get caught by this hook, and forced removal can tear the hook off. Do not pull the fish free; instead, submerge the net in the water, and it will free itself.
They require aquariums with ample open swimming space. Fishes prefer bright lighting. Aphyocharax species are schooling and peaceful, inhabiting the upper and middle water layers. When startled, they can jump out of the water and even glide some distance. They can be kept in a community aquarium, and the larger the school, the better they feel.
The aquarium should be elongated and covered from above, with plants and other decorations arranged to leave plenty of swimming space, as these fishes love open areas. The substrate must be dark. They are slightly more demanding regarding oxygen levels and aquarium volume than other characids. T 22-26°C; dH up to 20°; pH 6-7.5.
— Bloodfin Tetra, Anisitsi — Aphyocharax anisitsi [Eigenmann & Kennedy, 1903]. Synonym: Aphyocharax affinis, rubropinnis, Phoxinopsis typicus. (English: Argentine Bloodfin, Bloodfin Tetra, Glass Bloodfin, Red Finned Tetra, Characin). Northern Argentina, Paraguay, Paraná River. 4-5 cm. Body elongated, laterally compressed. Coloration is silvery-gray, acquiring a bluish or greenish tint depending on the angle of light. The back is greenish-purple, the flanks shimmer with yellowish, greenish, or blue hues.
All fins, except the pectorals and adipose, are blood-red (the caudal fin is colored only on the anterior half). Pelvic and unpaired fins are red or reddish with white tips. Their coloration is uneven: brighter at the base and usually fading towards the edges. In some individuals, the dorsal fin is very faintly colored. The female is paler, larger, and fuller. Sexing is quite difficult; males can only be distinguished from females during transfer when they hook their anal fin into the net. Males have more intense fin coloration.
Peaceful, hardy, and active. These fishes are very dynamic and in excitement may jump out of the aquarium, though this happens rarely. A spacious aquarium with bright lighting is preferred; they coexist well with other active species. Keep in schools of 5 or more; the larger the school, the better they feel and the more peacefully they behave. Their beauty is most striking in a large group within a spacious aquarium.
They inhabit the middle or upper water layers. Timid, which can cause them to lose their natural coloration—becoming faded and inconspicuous. The aquarium should be set up with dark tones. The substrate must be dark. Plants should be arranged mainly along the sides, leaving plenty of open swimming space, and the tank must be tightly covered with a lid. Filtration, aeration, and weekly water changes are required. They can even be kept in an unheated container.
The fishes are omnivorous, among the first to reach food, and eat eagerly and heavily, so they should be kept slightly underfed. Moderate feeding does not impair reproductive capabilities. They mature at 5-9 months. Breeding is relatively easy. They scatter eggs among plants. Suitable for beginner aquarists. Lifespan up to 8 years. pH 6.0-7.5; dH up to 16°; T 20-28°C.
Identification: Genus Aphyocharax — Aphyocharax anisitsi, dentatus.
— Emerald Tetra — Aphyocharax alburnus [Gunther, 1869]. Synonym: Aphyocharax avary. (English: Goldencrown Tetra). From central Brazil to Argentina. 7 cm. The fish has a strongly elongated bluish-silver body. An emerald-green longitudinal stripe begins behind the gill cover and extends to the tail. All fins except the caudal are colorless. The caudal fin can range from pale pink to reddish, with a small dark spot sometimes visible at its base. Females and males have identical coloration.
Easy to care for, very active, should be kept in a school in a community aquarium. Swims in the upper water layer. When kept singly, it chases other fishes and blocks them from food. Fine-leaved plants in the foreground provide sufficient open swimming space in the upper water layer. Under subdued light, the green longitudinal stripe is more distinct. Clean, oxygen-rich water is necessary, requiring a filter and strong aeration. Slender males engage in vigorous spawning displays. Cover the aquarium securely. Omnivorous, accepts live, dry, and frozen foods. Breeding and rearing are not always straightforward. Lifespan 5 years. pH 7.0; dH up to 20°; T 20-26°C.
— False Bloodfin, Dentatus — Aphyocharax dentatus [Eigenmann & Kennedy, 1903]. Synonym: Aphyocharax nasutus, pappenheimi, Notropocharax difficilis. (English: False Bloodfin, Red Tail Tetra). Paraguay, Colombia. 12 cm. Silver body with shades of green, blue, and brown. Adorned with a red caudal fin (the only one among all). Males are more slender, females fuller. Males have hook-shaped anal fins.
Very easy to maintain in a community aquarium. Plants should be arranged mostly along the edges, leaving ample swimming space. A fast, active schooling fish. Keep in a school. Generally stays in the middle or upper water layers with a moderate current. These are relatively cold-water fishes, thriving at 18-22°C for up to 10 years. At temperatures above 24°C, lifespan decreases. dH up to 25°; pH 6.0-7.5; T 15-22°C.
Aphyocharax erythrurus, Aphyocharax paraguayensis, Aphyocharax rathbuni.
Rachoviscus crassiceps, Xenagoniates bondi. 
