Mexican Tetra Care Guide - Aquarium Setup, Feeding & Breeding

The Mexican Tetra, Astyanax mexicanus, is a lively freshwater characin with a laterally compressed, silvery body and a deeply forked tail. Aquarium-bred surface forms often show a darker back, a subtle golden or greenish sheen and a dark mark near the base of the tail. Its streamlined shape reflects a fish built for life in flowing water and open stretches of river.

This species is best known for existing in both sighted surface populations and naturally blind cave populations. Cave forms have reduced or absent eyes and a paler, sometimes pinkish appearance, while their heightened senses of smell, touch and vibration help them navigate permanent darkness. Most aquarium specimens sold as Mexican Tetras are sighted surface forms, although the cave form is also kept by specialist aquarists.

Mexican Tetras are active, alert schooling fish that spend much of their time in the middle and upper areas of the aquarium. They investigate their surroundings constantly and can display quick bursts of speed, especially when feeding. In a group they are generally confident and entertaining, although individuals may occasionally chase one another or nip at fins.

In the wild, the species occupies rivers, streams, pools and cave systems, with different populations adapting to very different conditions. Its ability to thrive in both sunlit and lightless habitats has made Astyanax mexicanus an important subject in studies of evolution, sensory biology and adaptation.

Mexican Tetras are native to freshwater drainages of eastern and central Mexico, including rivers that flow towards the Gulf of Mexico. Their wider natural range also reaches the lower Rio Grande region of southern Texas, North America. Cave-dwelling populations are especially associated with underground waters in parts of Mexico.

A group of Mexican Tetras should have at least a 100-litre aquarium, with a footprint of about 90 cm long by 30 cm wide or larger to provide room for sustained swimming. Use open swimming space through the centre and foreground, with plants, roots or rocks around the edges to create cover and visual boundaries. A secure lid is advisable because this active species can jump. A sand or fine gravel substrate works well, while moderate water movement, efficient filtration and good oxygenation help recreate the clean, flowing habitats occupied by many wild populations. Surface-form fish appreciate subdued lighting softened by floating plants, whereas blind cave forms are best kept in dim or dark conditions.

Mexican Tetras can reach approximately 12 cm (4.7 inches) in total length. Females are usually deeper-bodied and may grow slightly larger than males, which are generally slimmer.

Mexican Tetras are omnivores and accept a varied aquarium diet. Offer a quality small-to-medium tropical flake or pellet as the staple, supplemented with frozen or live foods such as bloodworm, brine shrimp, daphnia and mosquito larvae. Occasional vegetable matter can be included, particularly for variety. Feed small portions once or twice daily and ensure every fish gets access to food without allowing excess food to accumulate.

Mexican Tetras suit a robust community aquarium containing similarly sized, active fish. Suitable companions can include larger peaceful tetras, rainbowfish, danios, barbs, livebearers, peaceful larger rasboras and bottom dwellers such as Corydoras and sturdy small catfish. Avoid very small timid fish, slow-moving species and long-finned fish such as bettas and fancy guppies, as Mexican Tetras may outcompete them for food or nip their fins. They should also not be housed with aggressive cichlids or fish small enough to be swallowed.

Mexican Tetras are egg-scattering spawners that can breed in a dedicated setup. Condition a group with plenty of live or frozen foods, then place it over fine-leaved plants, spawning mops or a mesh divider so the eggs are protected from the adults. Spawning usually occurs among the vegetation, with several hundred adhesive or semi-adhesive eggs possible. Remove the adults after spawning, and expect the eggs to hatch in roughly 24 to 36 hours. Feed free-swimming fry infusoria or another suitably tiny first food before moving them on to baby brine shrimp.

Females are typically larger, fuller-bodied and noticeably rounder through the abdomen, especially when carrying eggs. Males are usually smaller and more slender, and may develop a slightly more intense coloration when mature.