River garfish

Where they come from

River garfish (Zenarchopterus xiphophorus) are those slim, surface-hugging halfbeaks you see in Southeast Asia. You will find them around slow rivers, canals, mangroves, and estuaries where fresh and salt mix. That brackish swing is a big part of why they can be touchy in a plain freshwater community tank.

Setting up their tank

Think "long and calm at the top." These fish live at the surface, pace a lot, and they startle easily. A long footprint matters more than raw gallons. I would not keep a group in anything shorter than a 3 ft tank, and 4 ft makes them look way more relaxed.

• Tank size: 30-40+ gallons for a small group, but length beats height every time
• Group size: 6+ if you can, they act less jumpy in a proper group
• Flow: gentle to moderate, avoid blasting the surface like a river-tank setup
• Lighting: not too harsh, floating plants help a ton
• Cover: tight-fitting lid, tape over gaps around hoses and wires

Brackish water is where most people either nail it or slowly lose fish. I mix marine salt (not aquarium tonic salt) in a bucket with a small pump, then add it to the tank. For river garfish, I have had the best luck around low to mid brackish (roughly SG 1.005-1.010). Stability matters more than chasing a perfect number, so pick a target and stick with it.

• Use marine salt mix and a refractometer or hydrometer (refractometer is way easier to trust)
• Aim for steady salinity, do not swing it up and down week to week
• Temperature: mid-70s to low-80s F (24-28 C)
• Keep nitrogen low: they are not fans of dirty surface film and high nitrates
• Leave open swimming space at the surface, but add cover around edges

Decor wise, I keep it simple: sand or fine gravel, some hardy brackish-tolerant plants (if you can keep them), and lots of floating cover. They like to cruise the top edge of the tank and hover under floaters. If the surface is wide open under bright lights, they stay skittish and hide in corners.

What to feed them

They are surface micro-predators. That beak is built for snatching insects and tiny critters off the top. New imports often ignore flakes and pellets at first, and some never really take to them. Live and frozen foods make life easier.

• Best starters: live or frozen mosquito larvae, daphnia, brine shrimp, cyclops
• Reliable frozen: bloodworms (not as a staple), mysis, finely chopped krill
• Good live options: small crickets, fruit flies, gnat-sized insects (avoid pesticide risks)
• If you want pellets: try small floating predator pellets and train slowly alongside frozen

Watch their bellies. A healthy river garfish should look sleek but not pinched. If you see hollow bellies or a fish hanging back at feeding time, bump up feeding frequency and make sure food is reaching everyone. I usually do smaller meals 1-2 times a day rather than one big dump.

How they behave and who they get along with

These are alert, fast, surface fish. They are not generally aggressive, but they are competitive at feeding and can harass smaller surface fish. Males can bicker and chase, especially in a small tank or if the group is male-heavy.

• Temperament: active, easily spooked, mostly peaceful but pushy at mealtime
• Tank level: top and upper-midwater
• Best kept: in groups with plenty of surface cover
• Expect: lots of surface cruising, occasional sparring, and quick darting when startled

Pick tankmates that like similar brackish water and will not bully them. Avoid anything that nips fins or constantly charges the surface. Also avoid tiny fish that can fit in that mouth. They might look delicate, but they can inhale surprisingly big snacks if it fits.

• Good options: brackish mollies, bumblebee gobies (with a peaceful setup), knight gobies (in a larger tank), some brackish-tolerant rainbowfish depending on salinity
• Use caution: archerfish and monos (often too boisterous and outcompete them)
• Avoid: fin-nippers (many barbs), hyper-aggressive cichlids, very small livebearer fry you want to keep

Breeding tips

Breeding river garfish in home tanks is possible, but it is not like breeding guppies. They are livebearers (halfbeaks), and females carry developing young for a while. The trick is getting well-conditioned adults, keeping them steady in brackish, and giving the babies somewhere to hide because adults will pick off fry.

• Keep a bigger group so you get both sexes and reduce nonstop male attention on one female
• Condition with lots of small live/frozen foods
• Provide thick floating plants or spawning mops at the surface for fry cover
• If you want to save fry, move the female near dropping time or pull the fry as you spot them

Common problems to watch for

Most issues I have seen come down to three things: wrong water type (kept in straight fresh), injuries from jumping, and slow starvation because the fish never fully switches onto prepared foods.

• Jumping injuries: scraped beaks, missing scales, sudden death after a "thump" - fix lid gaps and lower stress
• Chronic sickness in freshwater: repeated ich/velvet/bacterial issues - move to stable brackish and clean up water quality
• Starvation: fish looks thin or "knife-bellied" - offer more live/frozen and spread feedings out
• Mouth/beak damage: can happen from glass surfing or panic-dashing - add floaters, reduce reflections, avoid bright bare tanks

Also keep an eye on surface scum and low oxygen at night. A heavy plant load plus warm brackish water can mean low oxygen by morning. I like a gentle sponge filter or an airstone aimed so it ripples the surface without turning it into a washing machine.