San Luis Potosi Pupfish

Potosi Pupfish (Cyprinodon alvarezi)

A critically rare and conservation-priority pupfish from the isolated spring system of El Potosí in Nuevo León, Mexico. Named after the renowned Mexican biologist and ichthyologist Dr. José Álvarez del Villar (1903–1986), this species is now Extinct in the Wild and survives only through dedicated captive breeding programs. Its small size, unique evolutionary history, and the urgent need for ex-situ conservation make it one of the most significant species in the aquarium hobby for those interested in preserving biodiversity.

Key Features

• Maximum Size: 5.0 cm / ~2.0 inches TL.
• Appearance: Compact, fusiform body typical of desert pupfishes. While specific wild coloration is not extensively documented in available data, males often display more vibrant hues during breeding, with the overall pattern suited to their spring habitat.
• Fin Details: Dorsal soft rays 10–12; anal soft rays 9–11.

Aquarium Care

• Tank Size: Minimum 20–30 gallons for a small group (species tank strongly recommended).
• Water Parameters: Subtropical to warm temperate; 64–72°F (18–22°C), pH 7.5–8.5, moderate to hard. Excellent water quality with stable parameters is critical. Provide a sandy or fine-gravel substrate with some rockwork and minimal vegetation to mimic their natural spring environment. Gentle filtration and regular partial water changes are essential.
• Diet: Omnivorous — accepts high-quality flakes, micro-pellets, and small live or frozen foods (brine shrimp, daphnia, bloodworm). A varied diet supports health and breeding.
• Behavior: Generally peaceful but best kept in species-only or carefully planned setups due to its rarity and specific needs. Not a seasonal killifish; active year-round in appropriate conditions. Breeding is possible in captivity but requires attention to water quality and diet. This species is considered difficult to maintain long-term compared to more common pupfishes.

IUCN Status Extinct in the Wild (EW)