06-02-2009, 03:55 PM
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Hatchetfish, like almost all of the characins (tetras, pencilfish, headstanders...) to which group they belong, are shoaling fish and do best in groups. The number depends upon your tank space, but a minimum of 5 or 6 is recommended. There are three genera, Carniegella, Gasteropelecus and Thoracocharax. The species in the Carniegella genus are the smallest (rarely over 1 inch) and in my personal view the nicest; it includes the two species of marble hatchetfish, the black-winged hatchetfish (1 or 2 species, depending upon which author), and the pygmy hatchetfish. I have maintained all of them for many years. In general, they will do well in the same tank conditions as cardinals and other tetras. Contrary to what one still reads, they do not prefer strong filter currents; given the opportunity, in my experience they will avoid currents and remain in the quieter areas among floating plants (a must). Ceratopteris (floating Indian fern) is ideal even though an Asian plant. In their natural environment, hatchetfish live in groups among overhanging vegetation and roots and branches.
They will jump through the smallest opening, so the tank must be covered to the point of leaving no openings beyond what is necessary for the filter tubes and heater units. Like their tetra cousins, they prefer soft slightly acidic water, and are somewhat less tolerant of adverse water chemistry. Some authors say live food is mandatory for part of their diet, but except during the 1980's I have never provided live food and have had all five species of Carniegella thrive for years. I think the longest lived marble hatchet I've had was 7 or maybe 8 years in my tank. They readily eat flake food, but do get a bit more excited with prepared foods like bloodworms and flies, and frozen bloodworms are a treat. Food has to float for hatchets.
I have always considered hatchetfish a "must have" in one of my SA aquaria, they are very interesting fish and when conditions are to their liking they regularly display play and spawning behaviours, though I have never seen actual spawning probably due to non-live foods. They are the only true flying fish; studies have proven that they do actually "flap" their pectoral fins much as hummingbirds do, and can leave the water and "fly' for more than 12 feet. Gery opinioned this behaviour is to escape a predator rather than catching aerial insects. I have noted that if they are startled by something in the aquarium, they will "take flight" and sometimes even bump into the cover glass, though this is not frequent and never fatal in my experience. But as noted above, the tank must be covered; I have had them jump out and onto the floor when doing a partial water change.