Montezuma Swordtail

Adult males reach 4–5 cm in length, not counting the tail. The tail's elongated lower rays form the characteristic "sword", which can be twice as long as the fish's body. Males have a silvery body, often with yellow or greenish iridescence. Several black spots appear on the body, most notably on the dorsal fin. Females are similar in size but have duller, mostly grey coloration. A distinct black stripe runs along the entire female body from head to tail. Females lack the prominent sword of the males.

These fish naturally inhabit the northeastern regions of Mexico. They prefer river systems that flow from hilly terrain toward the Gulf of Mexico. Montezuma swordtails are often found near the shoreline, hiding among dense aquatic vegetation.

Males of this species are temperamental and often compete with one another for territory and female attention. In a small tank, keep them in a harem: one male with several females. They are peaceful toward other fish species. Montezuma swordtails are compatible with many freshwater species of similar size and temperament. Avoid keeping them with fin-nippers such as certain barb species.

A tank of 100 litres suits a group of 4–5 montezuma swordtails. Provide refuges: dense patches of live plants, driftwood with branches, or artificial decorations. This species is undemanding in care. Maintain slightly alkaline water with moderate to high dGH. Weekly partial water changes and a reliable filter keep organic waste low. Moderate water flow created by an efficient internal filter mimics the natural river conditions.

They accept any aquarium foods. Their daily diet may include dry flakes or granules, supplemented with live or frozen brine shrimp, bloodworm, daphnia and other small invertebrates.

Under good conditions and with balanced feeding, spawning occurs every 4–6 weeks, with the same interval for incubation. Montezuma swordtails are livebearers: females produce fully formed fry. A single female usually delivers 10–30 fry. The fry can feed within an hour of birth. These fish lack parental instincts and may eat their own young.

Disease risk increases if the fish are kept in unsuitable conditions, fed poorly, or injured. In conditions close to their natural habitat, illness is very rare.

When choosing montezuma swordtails, check their activity and skin condition. Healthy fish should be curious, swim actively, and show no visible damage, sores, or white coating on the scales. Avoid fish that stay at the surface, breathe heavily, or have clamped fins—these signs indicate poor water quality or infection. Check the fins: they should be whole, with no splits or erosion. Observe behaviour: males in the shop often display territorial conflicts, which is normal. Look for signs of condition: the belly should not be sunken, and the body should match species standards with no spine deformities.