The Hatchet Fish, Carnegiella strigata

Hatchet Fish the flying fish of the aquarium
Thomas R. Reich, PhD

Of the Genus commonly referred to as Hatchet Fish, a total of three species are known, Carnegiella myersi, Carnegiella marthae, and Carnegiella strigata, of which only Carnegiella strigata is commonly known and represented by not less than five sub-species, which we commonly see today in aquarium stores.

The Hatchet Fish are distinguished from all other fish by the remarkably deepened belly which from the top cannot even be easily seen since they are so thin, but from the side, the lower portion of the fish looks like a huge pot belly.

In fact, not less than a fourth of the total weight of the fish is included in these muscles contained within what looks like a belly. 

The Hatchet Fish are thus able to make long gliding flights using their powerful “wing-like” fins over the water in nature. This “flight” is made easy by the extremely compressed sideways, almost ax-sharp “prow”. They do not really fly by moving what look like their “wings” up and down in the air (nor, to be sure, does any other kind of a “flying fish” in the ocean either), but more on this later.

It is truly unfortunate that we do not get to see these fish even try their flying tricks today in the aquarium, they have been bred in captivity for so many generations, they have lost the will to even attempt the feat. 

The basic coloration is brownish to golden yellow with a silver sheen; the back is more or less dark green with black dots of varying size. The flanks are covered with a pattern of spots of a typical pink to brown, changing to light blue.

A pair of dark stripes may be seen on the sides if the head; from the gill covers to the caudal fin runs a black lateral line, bordered on the upper side by a gleaming silver stripe.

From the edge of the belly run three irregular, dark blue to brownish black stripes angling forward and backward across the body.

The streak lying above the anal fin is also blackish. The fins are light greenish and transparent. The caudal fin is clearly green. External sexual characteristics are unknown. When not in prime breeding condition, or one is not observing closely, many Hatchet Fish simply appear silver. This is partly due to slightly different stains in color lines, part due to inbreeding, part due to observation technique.

Interesting Note in History

In 1937, Dr. Hoedeman had several specimens (Carmegiella strigata) to care for and he had an extra large aquarium available for them – 150 gallons or about 5 feet in length.  As a precaution, the tank edges above the water surface were cushioned with sponge rubber so the Hatchet Fish would not damage themselves if they attempted to “fly” as they did in the wild.

The Hatchet Fish did try to fly several times and simply bounced off the sponge rubber protection during the first few days. These fish had come directly from their natural habitat which was Guianna, in South America. The fish learned quite quickly, (however they showed no fear of hitting the sponge rubber) that there was limited space and that flying space was not available. After about 48 hours of attempts, the Hatchet Fish never attempted flight again, though they lived for some years after that first day.

Place of Origin

The Hatchet Fish was discovered in marshes, flooded regions, in brooks, ditches, small and large rivers all over The Guianas, and the central and lower reaches of the Amazon drainage basin, especially in jungle streams. As a rule in nature, they are close beneath the surface where they like to lie among marsh and water plants. In nature, they are insect eaters, and larva eaters, and very effective in keeping mosquito populations down

What makes the hatchet fish unique among the aquarium fish?

When you think of flying fish, you think of the fish that inhabit the warm waters of the Atlantic and Pacific Oceans. You may have seen them in movies, TV shows or within the pages of National Geographic. Their ability to glide through the air is so well developed that their flights occasionally carry them onto the decks of ships.

Few people, however, know about the amazing little freshwater flying fish, better known as Hatchet Fish. Many aquarists who keep these popular fish in aquariums have never heard of their flying ability, which is really quite remarkable for their small size.

Hatchet Fish fly at least as well as the better known marine flying fish. Hatchet fish can propel themselves through the air from fifteen to twenty feet or more, while the flights of marine flying fish, which are many times larger, rarely exceed two hundred feet. Furthermore, it has been proven that Hatchet Fish actually propel themselves through the air by flapping their pectoral fins (their “wings”}. Marine flying fishes use their fins only for gliding.

What advantage is flight to fish?

Observing Hatchet Fish in nature, the answer is readily apparent: it is most often a means of escaping from enemies. Hatchet Fish swim in groups just under the surface of the water, where they are continually searching for insects and small aquatic animals. When a larger fish approaches to eat them, the Hatchet Fish are in the air and far away from danger in an instant.

Hatchet Fish get their name from their peculiar shape. From the side, they look like deep triangles, rounded only at the bottom, not unlike the shape of a hatchet. From the front, they are thinner than a cracker, tapering to a knife edge along the belly. It is pretty well established that the proportionately deep body contains large muscles that contribute to the fish’s ability to flap its fins in flight.

How To Keep Hatchet Fish Happy

Hatchet fish are a very popular addition to most aquariums, however, it is important to remember that this is a warm water fish. It will not live long below 75 F and prefers 78 F to 82 F like many of the true tropicals in a community aquarium. 

This unusually shaped, ornamental fish requires a well-planted aquarium with clear water at a temperature of 75F-86F (I cannot repeat this enough, they will simply die in water that is less than 75 F).

It is very tolerant and can be kept without danger among all species of fish of about the same size. In any case, it is advisable to have a large aquarium at its disposal, considerable sunlight or well lit with good led or compact fluorescent light, and plants that grow up to the surface of the water to simulate their natural environment.

Hatchet Fish are shoal fish, which means they like to be kept in a group of 3 or 5 or 7 and like to have a grouping of rocks and plants to swim around. Putting these unique fish in a bare tank will make them very unhappy, insecure, and they will not survive long. They need live plants, rock outcroppings and room to swim, but they are good tank mates with other small and medium community aquarium fish, if they fight among themselves it is only a form of play, no harm ever comes of it.

It should go without saying that any aquarium containing Hatchet Fish should be covered with a full aquarium hood, this is to avoid unscheduled flights. It is unlikely that the fish that you buy in local stores, which were bred in captivity would try to fly, but do not take the chance, it has been known to happen.

Breeding

Spawning is possible but not common. This is a very difficult fish to breed and is only to be attempted by an expert breeder or someone who really wants a challenge, and has the time, space and patience to try.

The act of breeding occurs among the roots of plants along the surface of an aquarium at simulated dusk or natural dusk of a tank that is lit by natural sunlight. Spawning also may occur by simulated moonlight also among the roots of plants floating on the service of the aquarium. Remember that temperature is very important, 86F is best, to simulate late spring/early summer in nature.

The males do a fluttering dance parallel to the females on the shoots of finely feathered plants under the water’s surface. The eggs cling to these fine-leaved plants. The rearing of the fry, which hatch after 24-30 hours, is not difficult with rotifers (infusoria) and later baby brine shrimp and fine baby food.

Naturally the parents must be removed after spawning has occurred; however, Hatchet Fish are not egg eaters, so timing is not as critical as with tetras or barbs. The parents will actively eat the fry as soon as they hatch, just as they would any larva they find in the water so they must be removed as soon as possible after spawning. Make sure plants and tank are snail free, remember eggs are a snails favorite food.