Boeseman's Rainbowfish

Origin and Conservation Status:

This species is endemic to a very small area of West Papua (the Ajamaru, Hain, and Aitinjo lakes). Due to incredible catching pressure for the aquarium trade (now banned but plagued by poaching) and introduced alien species, the species is highly endangered in nature. Fortunately, today's commercial strains are mass-bred in captivity (Eastern Europe and Asia).

Sexual Dimorphism:

The dimorphism is extreme. Females are noticeably smaller, less deep-bodied (less humped), and maintain a uniform silvery-green livery with only a faint yellow or orange reflection on the fins. An all-male aquarium is not recommended: it is precisely the presence and competition for females that triggers the dazzling colors of the males, which will display a bright neon "flash" line on their heads during courtship.

Tank Setup:

The fundamental rule for Rainbowfish is not water chemistry, but swimming volume. They are tireless athletes. An adult M. boesemani (11 cm / 4.5 inches) confined to an 80 cm (30-inch) aquarium will waste away from stress. They require tanks of at least 120 cm / 4 feet (ideally 150 cm / 5 feet) with the central third left completely empty of decor. The sides and back can be densely planted with Vallisneria or Java Ferns to provide shelter. The tank must be tightly covered, as they are excellent jumpers, especially during courtship.

Diet and Coloration:

Do not judge a Boesemani by the dealer's tank. Juveniles are silvery and washed out. To ignite the spectacular blue and orange coloration (which takes up to 1 year to fully develop), the diet must be top-notch. They have a relatively narrow throat for their size: provide small floating pellets, crushed freeze-dried krill, and, above all, live or frozen food (mosquito larvae, mysis). Natural carotenoids (Astaxanthin) are essential for the red of the tail.

Water Quality:

Originating from karstic lakes, they love hard water, making them the perfect fish for those with naturally mineral-rich tap water (pH 7.2 - 8.0). They tolerate high temperatures if well oxygenated. However, their susceptibility to opportunistic bacteria increases drastically if nitrates are not kept very low with massive water changes (40% weekly).