Marbled hatchetfish

The marbled hatchetfish (Carnegiella strigata) is a small, 3.5 cm (1.4 in) in length, freshwater ray-finned fish. The small deep-bodied fish, in the genera Carnegiella, is from the family Gasteropelecidae which includes both Gasteropelecus and Thoracocharax. Native to South America, C. strigata can be found in the Caqueta River in Columbia, the lower, middle, and upper Amazon River Basin, south of Amazon, and can be found in rivers and streams all throughout Northern South America.^[3]

Marbled hatchetfish
Carnegiella strigata lateral view
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification (accepted)
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	Gasteropelecidae
Genus:	Carnegiella
Species:	C. strigata
Binomial name
Carnegiella strigata (Günther, 1864)
C. strigata's native distribution
Synonyms[2]
Gasteropelecus strigatus Günther Gasteropelecus fasciatus Garman Carnegiella vesca Fraser-Brunner

Morphology

Hatchet shaped, with a laterally compressed body, it presents a gold line extending from its eye to its caudal fin while the area below has a brown and cream colored marble-like pattern (hence its name). Along its sides, the marbled hatchetfish has distinctive wing-like pectoral fins which allows them to “jump” out of water. This adaptation is like flying fish found in the ocean, yet smaller sized. The C. strigata has a very small dorsal fin located near the base of the caudal fin, and it plays a minimal role in its movement. The caudal fin is short, used for stability and control while it slowly swims along the surface. They also have an upturned mouth used for surface feeding floating at the water’s surface. Female C. strigata tend to have larger abdomens compared to males because of their reproductive organs. There are two sub species which are recognized as “two forms”: Carnegiella strigata and Carnegiella fasciata. They differ by their marbling patterns, strigata contain V-stripes and fasciata contain Y-stripes. Marbled hatchetfish are adapted to life in the Amazonian rivers as they resemble a dead leaf floating sideways on the surface of a body of water. This camouflage protects them against potential predators that may be lurking in the water. Their marble-like pattern is to give the illusion of rays of light breaking the waters surface and reflecting on the portrayed leaf. The fish itself does not move much, letting the waves and current move it mostly, but with occasional brief twitching movements. This replicates the way a leaf would be blown around or carried away by the tide or a current. The line running from its eye, to its tail, is believed to replicate the midrib (midvein) of a leaf.

Two distinct morphological types of Carnegiella strigata described by Géry. (1973): (a) intermediate form and (b) strigata form.

Diet

The C. strigata, has a superior mouth, optimal for surface feeding. Their diet primarily consists of various zooplankton and small insects.^[4] To feed and to avoid predators, C. strigata, can propel itself out of water by flapping its pectoral fins.

Habitat

In the Rio Negro region, the marbled hatchetfish lives in habitats called igapo and igrape. These habitats include dense riparian vegetation, overhanging branches, and leaf litter. During wetter seasons the water levels along the river can rise up to 15 meters.

In the aquarium

The marbled hatchetfish is common in the aquarium industry. It represents one of the largest exports of freshwater ornamental fish from the Rio Negro Region with about 400,000 exported annually. Like most Amazonian fish, the species prefers softer, acidic water within the pH range of 5.0 to 8.0. As with most characins, they are omnivores. Hatchets have a tendency to be shy fish and are easily intimidated by larger or fast moving fish, so they are only appropriate for very peaceful communities or species tanks. The marbled hatchetfish is usually kept in small schools. Groups of more than 5 individuals are ideal within a minimum tank size of 80cm. It is necessary for tanks inhabited by these fish to have a tight lid, as they are known to jump out of tanks lacking lids when startled.^[5] Marbled hatchetfish are egg-scatterers and have been bred in the aquarium hobby. Within captivity, the marbled hatchetfish can live up to 5 years. In studies done in the past, the marbled hatchetfish can withstand different environments for short periods without too much stress induced. This was mainly done from the high demand of ornamental fishes, and because they are easy to care for, marbled hatchetfish are low maintenance. With their small size and simple diets they are ideal for the aquarium.

See also

• List of freshwater aquarium fish species