Feathered river-garfish

Where they come from

Feathered river-garfish (Zenarchopterus dispar) are halfbeaks from Southeast Asia. You will see them around estuaries, mangroves, and slow coastal rivers where fresh and salt mix. That brackish lifestyle explains a lot about what they like in the tank: moving water, open space at the surface, and stable salinity.

Setting up their tank

Give them length more than height. They cruise the top like little torpedoes and they spook fast, so a long footprint makes a bigger difference than a tall tank. A tight lid is non-negotiable. Halfbeaks jump, and this species is no exception.

• Tank size: I would not bother under a 30 gallon long for a small group. Bigger is easier because it spreads out the chasing.
• Group size: 6+ works better than a pair. With only a couple, one fish usually gets picked on.
• Salinity: Brackish. I have had the best luck around SG 1.005-1.010, kept steady with marine salt (not freshwater aquarium salt).
• Temp: mid to upper 70s F is a comfortable range. Keep it stable.
• Flow and filtration: moderate flow and good surface movement. They like oxygen-rich water up top.
• Decor: open swimming lane at the surface, plants or roots along the sides, and some shaded spots so they feel secure.

For substrate and hardscape, keep it simple. Sand looks natural and is easy to clean, but they do not care much as long as the surface zone is open. If you want plants, lean into brackish-tolerant stuff (Java fern attached to wood can work in low-end brackish, and some people use mangrove-style root decor for cover).

What to feed them

These fish are surface hunters and they have small mouths for their size. Mine ignored food that sank fast and did best on floating or slowly drifting foods. If they are new, expect them to be picky for the first week or two.

• Great staples: frozen mysis, brine shrimp, chopped krill, finely chopped prawn, and good floating micro pellets once they recognize them as food.
• Live foods (great for getting them started): adult brine shrimp, mosquito larvae (if you can collect safely), and small insects.
• Feeding style: small meals 1-2 times a day. They do better with frequent little feeds than one big dump.

Watch their bellies from the side. A well-fed halfbeak looks gently rounded, not pinched. If you see skinny fish and one or two that look great, it is usually a feeding access problem at the surface, not a mysterious disease.

How they behave and who they get along with

They are busy, alert, and a little twitchy. They spend most of their time in the top few inches and will dash if something startles them. In groups they settle in and look much more natural, but there will still be some sparring.

• Temperament: semi-peaceful. Not a bully like some brackish predators, but they will pick at each other and may chase small surface fish.
• Best tankmates: brackish peaceful-to-moderate fish that use the middle and bottom (bumblebee gobies in low-end brackish, knight gobies with care, some mollies, and other calm brackish community choices depending on salinity).
• Avoid: fin-nippers (they stress easily), very tiny fish (might get harassed), and big aggressive brackish fish that will dominate feeding.

They also do best in a calmer room. Constant foot traffic and sudden light changes can keep them jumpy. I like to run a gentle ramp-up light or turn on the room light first before the tank light.

Breeding tips

They are livebearers (like other halfbeaks), which is the fun part. The tricky part is getting a stable, well-fed group and then protecting the fry, because adults will snack on babies if they get the chance.

• Sexing: males are usually slimmer and have a modified anal fin (andropodium). Females are deeper-bodied and often look more rounded when gravid.
• Setup: a well-planted or heavily structured edge zone helps. Even simple clumps of fine cover at the surface give fry somewhere to hide.
• Feeding the parents: varied meaty foods and consistent meals make a big difference in how often you see drops.
• Fry care: move fry to a separate rearing tank if you actually want to raise many. Start with baby brine shrimp, microworms, and fine crushed foods they can take at the surface.

Common problems to watch for

Most issues I have seen with this fish come down to three things: unstable salinity, not enough surface-oriented food, and stress from a bad social setup.

• Jumping: the classic halfbeak problem. Use a tight lid, cover gaps around hoses, and keep the waterline a bit lower.
• Slow weight loss: usually food competition or the food sinking too fast. Adjust feeding and spread food along the surface.
• Shyness and skittishness: often caused by too small a group, too bright lighting with no cover, or aggressive tankmates.
• Fin damage from sparring: more common in cramped tanks. More space and more cover usually calms it down.
• Brackish mismatch: keeping them in straight freshwater long-term tends to lead to chronic stress and recurring health issues.

If you keep the surface zone open, feed like you mean it, and treat salinity as something you measure and hold steady, Zenarchopterus dispar are really rewarding. They have a cool, nervous energy, and once they settle in they are constantly doing something interesting up top.