Mediterranean killifish

Geographic Origin and Biotope: Endemic to the Mediterranean Sea basin (Italy, Greece, North Africa). Populates the brackish waters of lagoons, estuaries, salt pans and coastal swamps subject to extreme thermal and salinity excursions.

Taxonomy and Morphology: Mediterranean Killifish (Aphanius fasciatus). Small, stocky and robust cyprinodontiform. A "relict" species adapted to survive in extreme conditions (euryhaline and eurythermal). Small mouth turned upwards to catch mosquitoes.

Social Behavior: Gregarious, lives in large schools that incessantly patrol the surface of the water. Males are exhibitionist and vivaciously territorial towards other males, competing for the favor of the female school.

Coloration and Sexual Dimorphism: High dimorphism. Females are uniform olive-green with faint gray vertical stripes. The breeding male "lights up": dark metallic gray background, jet black dorsal fin and bright silvery-blue zebra stripes (hence "fasciatus").

Aquarium Setup: Specific brackish water tank (minimum 80 cm / 32 inches for a school). Shallow water and wide swimming surface. Sandy bottom with macroscopic algae (Caulerpa) or dwarf mangroves. Tank cover useful against jumps.

Diet and Feeding: Essentially carnivorous micro-predator. Its primary meal in nature is mosquito larvae, which is why it is very useful as a biological controller. In the aquarium it accepts crumbled flakes, daphnia, brine shrimp and bloodworms.

Water Quality: Withstands impressive thermal variations (from 10° to 35°C / 50° to 95°F in nature), although a range of 15-28°C (59-82°F) is ideal in the tank. The addition of marine salt is crucial (salinity 5-25 ppt). In pure fresh water, their immune defenses collapse.

Compatibility and Tankmates: Due to its needs for brackish and alkaline water, it must be kept in dedicated (monospecific) tanks. They tolerate pairing with wild Mollies or brackish gobies (e.g. Brachygobius).

Aquarium Reproduction: Quite simple. During the summer (warm temperatures), males attract females into the thick of the algae (Mop). Females lay viscous eggs adhered to the vegetation every day. Parents prey on their own offspring if malnourished.

Risks and Diseases: Extremely sensitive to Oodinium and fungal infections if forced into fresh water for prolonged periods. A constant salt intake is the only preventive medicine they need.