Carnegiella strigata strigata or marbled hatchetfish. One hatchetfish is not a marbled one (picture below). This is the only survivor of my old tank. Four others jumped out of the tank through an opening in the lid.

The hatchetfish here seen from above. Just under the water surface they're looking for insects that are close to the surface.

Three fish on the bottom of the tank. Somehow they have not quit got used to the open tank. As soon as they spot a person in front of the tank they go down.

Carnegiella strigata strigata

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Habitat: South America (Amazon)
Length: up to 2,5 inch (6,5 cm)
Temperature: 79-83 °F (26-28°C)
pH: 6 - 7
DH: 2-15°