Axelrod's rainbowfish

Geographic Origin and Biotope: Endemic to the Yapsei river (a tributary of the Sepik) in Papua New Guinea. Lives in a narrow river basin covered by calcareous forest: the waters of the stream are hard and alkaline.

Taxonomy and Morphology: Axelrod's Rainbowfish (Chilatherina axelrodi). Reaches 10 cm (4 inches), laterally compressed body and pointed snout-dorsal profile. Large and rigid scales compared to other genera.

Social Behavior: Feverish swimmer, rarely relaxes. Like all Melanotaeniids it needs a hierarchical structure within a large school (more males in exhibitionistic competition distract a single male from oppressing the females).

Coloration and Sexual Dimorphism: Iridescent males: yellowish-brown back, lower half of the body with a thick fragmented black-blue lateral bar emerging behind the pectorals. Bright yellow odd fins. Silvery or greenish, drab females.

Aquarium Setup: Minimum 120 cm (48 inches) given the hyperactivity and sudden accelerations. Excellent use of calcareous pebbles to keep the pH high, combined with strong currents (movement pumps) and rocks surfacing.

Diet and Feeding: Voracious omnivore of mid and high tank. Flake foods with a strong plant component (Spirulina, Chlorella) recommended, supplemented with frozen krill or bloodworms.

Water Quality: One of the freshwater species that most needs dissolved minerals: pH 7.5-8.2 and high hardness (GH 10-18). Using reverse osmosis for this fish will lead to the collapse of its immune defenses.

Compatibility and Tankmates: Ideal companion for community tanks of hard water fish, even mild Central American Cichlids or not too fierce Victorian Cichlids. Perfect with Melanotaenia boesemani.

Aquarium Reproduction: The male flashes a luminescent stripe on its forehead ("blaze") during courtship, leading the female towards the moss skein (or wool threads). Large eggs but slow to hatch (up to 15 days at 25°C / 77°F).

Risks and Diseases: The absence of females in shops (because they are "ugly") causes many aquarists to buy only males. An all-male school will become hysterical, triggering stress pathologies (cutaneous bacteriosis).