Wrestling Halfbeak
Dermogenys pusilla
Zenarchopteridae
About
A slender livebearing surface specialist from the sluggish canals, drainage ditches, flooded fields and weedy ponds of South-East Asia, recorded from Thailand and Malaysia through to Java, and drifting into brackish mangrove fringes in the wet season. The fixed lower jaw juts forward like a needle beneath a short, hinged upper jaw, and the silvery body hangs almost motionless just under the film until an insect lands. Males are the smaller sex, carry a red or yellow flash in the dorsal fin, and settle disputes by locking beaks and wrestling — the behaviour that gave the fish its trade name.
Care
Give it a long, tightly covered tank with a large open surface, dense planting and floating cover around the edges, and almost no current — surface area matters far more than depth. Water should be hard, near-neutral to slightly alkaline and above all stable: it reacts badly to deteriorating quality and to sudden swings in temperature or chemistry, so use small, frequent water changes rather than large ones. Keep one male with three or more females, or several males in a tank long enough for a loser to retreat. Never house it with boisterous, fast or larger fish; a chased or startled halfbeak bolts into the glass and can break its beak, and it jumps hard enough that a tight lid is mandatory.
Diet
Feed only at the surface, in small amounts twice a day. Gut-loaded fruit flies are the ideal staple; rotate in frozen or live mosquito larvae, daphnia, cyclops and bloodworm. Floating micro-pellets or crushed flake may be refused at first but are usually accepted over time — offer them, but do not make them the whole diet.
Tankmate compatibility
Gets along with (37)
Possible with care (181)
Avoid (53)
Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Telling males from females
What works for this species, most reliable first.
- The gonopodiumDefinitive · from about 4 weeks old
Look at the anal fin, underneath and just behind the belly. In females it stays a broad triangular fan. In males it narrows into a rod and angles forward — that rod is the gonopodium, a rebuilt fin rather than an organ that appears from nowhere.
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Frequently asked questions
- What tank size does a Wrestling Halfbeak need?
- A Wrestling Halfbeak needs an aquarium of at least 80 litres (21.1 US gallons) with a footprint at least 80 cm (31.5 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Wrestling Halfbeak need?
- Wrestling Halfbeak does best at 23–29 °C (73.4–84.2 °F), pH 6.5–8.2 and a general hardness of 8–20 °dGH.
- What group size does a Wrestling Halfbeak need?
- Wrestling Halfbeak is a social species — keep a group of at least 4 so natural behaviour emerges and stress stays low.
- Is the Wrestling Halfbeak suitable for beginners?
- Wrestling Halfbeak sits in the middle of the difficulty scale — manageable for a careful beginner who has done the reading, but it has specific needs worth researching first.