Order Characiformes
Family Gasteropelecidae
Genus Gasteropelecus
— Silver Hatchetfish — Gasteropelecus levis [Eigenmann, 1909]. Synonym: Pterodiscus levis. Brazil, lower Amazon basin. 4 cm. Famous for its ability to glide through the air for distances of several meters. Coloration is silver and transparent. The male has a black spot at the base of the dorsal fin and a dark stroke at the base of the anal fin. Females are slightly larger and more rounded than males.
Peaceful, active, spends almost all its time near the water surface, although occasionally when threatened or during feeding it may move into the water column. Part of the surface (but not all) should be covered with floating plants to prevent jumping. Excellent jumpers, easily leaping out of a loosely covered aquarium. Requires a strong water current from the filter, against which it loves to swim. Does not like surface water circulation.
Shoaling fish, keep only in a group of 7 or more individuals. Well suited for community tanks with other small fish inhabiting different water levels. Ideal tankmates include tetras, neon tetras, and other small, peaceful fish from the Amazon. Prefers soft, slightly acidic water. A significant part of the diet should consist of frozen and live foods, such as bloodworms and daphnia. During initial acclimation, they may be slightly reluctant to accept dry foods, but can later be trained. Do not take food from the bottom. pH 5.0-7.0; dH 1-12°; T 24-28°C.
— Spotted Hatchetfish — Gasteropelecus maculatus [Steindachner, 1879]. Synonym: Thoracocharax brevis, magdalenae, maculatus. Panama, Suriname, Colombia, Venezuela. One of the largest representatives of this genus — 7-9 cm. Olive-silver, back is olive-brown, sides have a diamond-like sheen, with small dark spots on the posterior half of the body. They lack a distinct black horizontal stripe on the flank. The female is fuller than the male.
Peaceful, active, likes to glide along the water surface. Given their size and body shape, these fish can look impressive when kept in groups of 5-7 individuals. Unlike other closely related species, they stay more in the middle water layers rather than at the surface. They are also less prone to jumping out of the water. In the aquarium, these fish combine nicely with angelfish and discus, and can also be successfully kept with peaceful gouramis, loaches, or other non-aggressive fish of similar size.
Good water quality is important; best kept in soft, slightly acidic water with high oxygen levels. Does not like surface water circulation. Excellent jumpers, easily leaping out of a loosely covered aquarium. Part of the surface (but not all) should be covered with floating plants to prevent jumping. Distance to the cover glass should be 15-20 cm. Soft, slightly acidic water is beneficial. Very sensitive to excess organics. It is desirable that the diet contains as many insects as possible. Do not take food from the bottom. pH 6.0-7.0; dH 2-12°; T 24-28°C.
— River Hatchetfish, Silver Hatchetfish — Gasteropelecus sternicla [Linnaeus, 1758]. Synonym: Clupea sternicla, Gasteropelecus argenteus, coronatus. Upper and middle Amazon basin, Guyana, Peru, Venezuela, Trinidad. 4-5 cm. The fish stays in sunlit, oxygen-rich upper water layers. This unusual decorative fish attracts attention primarily due to its very original body shape.
Body strongly compressed laterally, with a straight back and an arched, wedge-shaped belly. Head is small, mouth is superior. The dorsal fin is set far back towards the tail, pectoral fins are large with highly developed musculature (their weight reaches up to 1/4 of the fish’s total body mass). Caudal fin is two-lobed. The river hatchetfish can jump out of the water and glide over the surface for up to 3-5 meters, rapidly beating and buzzing its pectoral fins.
The main body background ranges from yellowish to silver-gray; in well-lit areas, the fish appears silvery. The body below the longitudinal black stripe is silvery, the back is gray-yellow, pectoral fins are transparent, and their length is up to half the body length. Depending on the angle of light, colors can shift from iridescent green to shimmering blue. Three parallel stripes run from the rear edge of the gill cover to the caudal fin: two yellow ones and a dark one between them. Small black dots are scattered across the entire body.
All fins are transparent and colorless, the dorsal fin sometimes has a narrow dark leading edge. Unlike other hatchetfish species, sternicla is easy to distinguish by its silvery body background and a dark longitudinal stripe with silvery borders located behind the gill covers. Sexually mature females are much stouter than slender males. They feature a characteristic swelling in the posterior part of the body.
Peaceful and relatively hardy fish. Compatible with any peaceful fish. Spends most of its time in the upper water layers. Easily jumps out of a loosely covered aquarium. Should be kept in a school of 6 or more in a general, top-covered aquarium (the cover glass should be raised 8-10 cm above the water surface) with a length of 120 cm or more, featuring occasional planted areas and floating plants, but leaving a large open space for swimming.
Fish spend most of their time in the upper water layer, swimming calmly among plants. They constantly communicate with each other, often engaging in intraspecific skirmishes and chasing each other around the aquarium; keeping them in a group helps disperse this conspecific aggression. Lighting is bright. A strong current using a powerful filter is required, but they do not like surface water circulation. Soft, slightly acidic water is used. Very good filtration, powerful aeration, and weekly water changes are necessary.
Adapting to new aquarium conditions upon purchase can be difficult. They do not take food from the bottom, feeding exclusively from the water surface. Insects must be included in the diet. Keeping sternicla in an aquarium comes with some specific challenges. In the wild, this fish expends a large amount of energy; in an aquarium, due to a sedentary lifestyle, it quickly becomes fat and loses reproductive capability. To prevent this, a strong water current is provided: the fish constantly swims, expends much energy, and does not suffer from obesity.
Unlike smaller hatchetfish, these fish will swim across all water layers in the aquarium, and consequently, feeding them will not pose problems. They feed on various small insects, flies and their larvae, small bloodworms, and various dry substitutes. Fish take food only from the water surface or as it slowly sinks; they do not eat food from the bottom. Since they come from the wild, acclimation should be carried out in a quarantine tank. Reaches sexual maturity at 1.5 years of age. Lifespan is 3-5 years. This species is most commonly available in the trade compared to G. levis. T 23-27°C; dH 2-15°; pH 6.0-7.2.
Identification: Gasteropelecus sternicla.
Hemiodus gracilis, quadrimaculatus, unimaculatus.
Carnegiella marthae, myersi, strigata. 
