Pygmy Swordtail

About

The pygmy swordtail is the smallest and quietest member of a genus everyone already knows from the shop tank. Females reach about 4.5 cm and males about 3.5 cm, the body is lemon to lilac with a hard black lateral line, and despite the name there is effectively no sword at all — the male's is one or two millimetres, which is why the fish is often sold as the swordless swordtail. It comes from the Río Axtla and neighbouring rivers of the Pánuco system in north-eastern Mexico, over soft bottoms among stands of Sagittaria. Nothing about it behaves like a shop swordtail: it is shy, retiring and unusually fussy about clean water. Its real problem in the hobby is genetic. Xiphophorus species interbreed freely, and the genome survey of all 26 of them found hybridisation running right through the genus's history — so a pygmy swordtail sharing water with a swordtail, a platy or any other congener does not stay a pygmy swordtail for long.

Care

Give it a tank of its own. Forty litres suits a group of six to eight: heavily planted, gentle flow, spotless water and frequent small changes, because it is more delicate than its larger relatives and resents dissolved organics. Hold 23-26 °C, pH 7.0-8.0 and hard water at GH 8-18 — soft, acidic conditions are wrong for it. Keep three or four females per male and never a lone pair, or the male's constant courtship wears the female out. Above all, keep no other Xiphophorus in the same water, and buy with your eyes open: shop stock is often already crossed. If the fish in the tank are not all the same fish, it is no longer this species.

Diet

Omnivore with a tiny mouth: fine flake and micro-pellet plus brine shrimp nauplii, daphnia, cyclops and grindal worms, in small portions twice a day.

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.

Also in these lists

Similar species

Same category and the closest water parameters — if this species isn't quite it, start here.

Sold in Lithuania

These Lithuanian shops listed this species in their public catalogue (checked August 8, 2026). Stock moves — ask before you travel.

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Frequently asked questions

What tank size does a Pygmy Swordtail need?

A Pygmy Swordtail needs an aquarium of at least 40 litres (10.6 US gallons) with a footprint at least 60 cm (23.6 in) long — for this species, swimming length matters as much as raw volume.

What water parameters does a Pygmy Swordtail need?

Pygmy Swordtail does best at 22–28 °C (71.6–82.4 °F), pH 7–8 and a general hardness of 8–18 °dGH.

What group size does a Pygmy Swordtail need?

Pygmy Swordtail is a social species — keep a group of at least 6 so natural behaviour emerges and stress stays low.

Is the Pygmy Swordtail suitable for beginners?

Pygmy Swordtail 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.

Sources

• FishBase — Xiphophorus pygmaeus (Pygmy swordtail)
• Wikipedia — Xiphophorus pygmaeus
• British Livebearer Association — Xiphophorus pygmaeus (Hubbs and Gordon 1943)
• Du et al., bioRxiv — Phylogenomics analyses of all species of Swordtails (Genus Xiphophorus) highlights hybridization precedes speciation
• Shrimp and Snail Breeder — Xiphophorus pygmaeus detailed guide