Hatchetfish, whilst not the most colourful of fish, have a unique nature and appearance, creating a welcome contrast and focal point. The fish are peaceful, small, and interesting to observe, and on the condition that your tank provides safe surroundings, make excellent community fish.
The hatchetfish family (Gasteropelecidae) is part of the Characin group of fish, which includes the Tetras, Pencilfish, and Piranhas amongst others. The family can be split into three groups (genera) Carnegiella, Gasteropelecus, and Thoracocharax, with only a few species in each group.
The Carnegiella group contains the smallest fish, and C. myersi
is the smallest of all the hatchetfish, growing to no more than an inch (2.5cm) but is rarely seen for sale. This tiny fish also has the most transparent body with few markings except for a light speckling and darker topside.
The Black-Winged Hatchetfish C. marthae marthae, which occasionally turns up in batches of other hatchetfish as well as on sale as a species, is not much bigger and grows to around 3.5cm. The name comes from the darkened pectoral fins and black line along the underside of the body and whilst an interesting fish, this species is sensitive to water conditions and will only thrive in soft, acidic water.
The most popular of this group is the Marbled Hatchetfish C. strigata, and is also the most patterned, sporting black/brown broken patches on a silver body. There are two variations of this species; one has more silver with lighter marks whilst the other has more solid black markings. Both variations grow to around 4cm and although they prefer softer water, will do well up to a pH of 7.5 and medium-hard water providing they are well acclimated.
The Gasteropelecus group includes the Common Hatchetfish G. sternicla
, and the Spotted Hatchetfish G. maculates
. Of these, unsurprisingly, the Common Hatchetfish is most often seen for sale. Common Hatchetfish will grow to around 6cm, but are often confused with, and sold as, Silver Hatchetfish since there is very little to tell them apart, although Common Hatchetfish tend to have a more evenly curved underside.
The Silver Hatchetfish Thoracochax secures
, is the largest of the group, growing up to 8-10cm, so requires plenty of room in the aquarium. Both silver and common hatchetfish are the hardiest of the group, adapting to a wider range of water conditions and mixing well in peaceful community aquariums.
The odd shape of the hatchetfish is due to a large muscle attached to the pectoral fins, which is used to give the fish an immense and sudden burst of speed, allowing them to leap several metres above the water! This is used as an escape response in the wild both to evade and confuse predators, and whilst rarely used in the aquarium, if the fish are frightened for any reason, they may well leap from the tank. Interestingly, while the fish jumps from the water, they 'beat' the pectoral fins to gain additional height in the air, making them a true flying fish rather than just a jumper or glider.
It is very important to be thoughtful of the hatchetfishes visible environment, since these fish will only thrive if they feel safe in their surroundings. Being a surface dweller, this is the area of the aquarium that needs concentrating on. Hiding spots and cover are essential and are best provided by floating plants, if these are not suitable you can use artificial plants and fix them above the water line so they drape into the tank. A mass of cover is not essential, but at least a few patches should be available for quick retreats.
Hatchetfish will actually prefer to spend time at the surface out in the open, since in the wild this is where they would gain food, but it is the knowledge that should they need to, there are areas where they can retreat to which is important.
A little water movement is also appreciated, so the filter outlet should be placed in a position that creates both moving and still areas at the waters surface. In the event of the fish becoming spooked, a cover on the aquarium is essential to prevent any from jumping out.
Whilst the silver and common hatchetfish will adapt to moderately hard water, the majority of hatchetfish do best in soft, acidic conditions and are sensitive to bad water conditions so good filtration, low nitrates and regular water changes are essential.
Hatchetfish are a quiet shoaling fish and must be kept in groups (four minimum), their behaviour will vary slightly depending on the suitability of the environment they are kept in. Under correct conditions including hiding spots at the surface, areas of gentle flow, and peaceful tank mates, the fish will exhibit more confident and relaxed behaviour.
Knowing they are in a safe environment the fish will swim gently, both at the surface and several inches below, loosely shoal, interact with other fish, and show interest in the owner's presence in order to gain food. Under incorrect conditions however, the fish will be skittish, fleeing from any movement both in and outside the tank, stay within a few cm of each other at all times, and be prone to jumping from the surface. These are all signs of stress and under such conditions the fish are likely to become ill quickly.
Whilst well suited to a community tank, fish that are over active or boisterous should be avoided, unless they are species that remain in the lower regions of the tank. Small peaceful tetras, rasboras, barbs, and some livebearers all make good tank mates and any bottom dwelling fish can be mixed with no difficulties. Other surface dwellers should be chosen with care and only mixed providing there is plenty of room for both species. Surface dwellers of a similar size and nature can help to increase the Hatchetfishes confidence if they get along well.
Whilst many gouramies can be a little big or boisterous, small species such as dwarf, honey, sparkling, croaking, or chocolate gouramies all make good tank mates and being of similar shape, compliment the hatchetfish well. Pearl gouramies also have a suitable demeanour, although they are best mixed with the larger silver and common hatchets.
Most mature hatchetfish can be sexed fairly easily, with females being fuller bodied and males more slender, but are unlikely to breed in the aquarium and most specimens for sale are still wild caught. The most likely to spawn are the marbled hatchetfishes, and will do so in very soft, acidic water along with subdued lighting and surface vegetation. The eggs are either attached to floating leaves or dropped to the aquarium floor, and are an easy target for other fish so a separate breeding tank is essential.
Whilst many characins will do well on flake or dried foods, hatchets require a varied diet, of which only about half should be made up from dried foods (although dried foods are still important). Recreating their natural diet of small surface dwelling insects and aquatic organisms can be achieved by feeding small natural foods such as black or white mosquito larvae, bloodworm, daphnia, and mixed foods. Frozen foods are suitable but if your hatchets are not quick feeders or refuse to feed below the surface, freeze dried foods make a good floating alternative.
Providing your aquarium and its occupants qualify for a suitable hatchetfish environment, these are a very interesting and well-recommended aquarium fish, becoming a focal point in any community.