Ajamaru Rainbowfish (Melanotaenia ajamaruensis)
The Ajamaru Rainbowfish (Melanotaenia ajamaruensis) is a mysterious species with an interesting story to tell. It was first discovered in the 1950’s during an expedition to West Papua by Marinus Boeseman. If the name rings a bell, it’s no doubt from one of the most beloved species in this group being named in his honor, Boeseman’s Rainbowfish (M. boesemani). That fish was also discovered during this same collecting trip, and the two species would remain confused and intertwined for many years after.
Rainbowfish authority Dr. Gerry Allen described both species in a paper published in 1980, using the specimens collected decades earlier by Boeseman. These were said to have originated from a remote, mountainous region on the Vogelkop Peninsula known as the Ajamaru Lakes region. But, it would be years until these waters were again sampled and the colors of the these fishes could truly be appreciated.
In 1982, Dr. Allen, along with well-known fish collector Heiko Bleher, visited this region and successfully collected rainbowfishes alive, ultimately resulting in the populations found today in the aquarium trade. At the time, the beautiful blue and gold males of M. boesemani caused a sensation, but, apparently, the more drably colored females were initially mistaken for M. ajamaruensis. The differences between these two species are rather slight and relate to minor discrepancies in the number of fin rays and other morphological counts. The most readily observable trait to look for is the prominent lateral band seen in M. ajamaruensis, which is lacking in mature males of M. boesemani.
When it was eventually determined that there were in fact no M. ajamaruensis in Lake Ajamaru, the question was raised… where exactly did Marinus Boeseman collect this fish from a half-century earlier? The answer wouldn’t come until 2007, when an expedition finally found this long-lost species in the nearby Kaliwensi River, located 5 km to the west of the lake. The two bodies of water are only indirectly connected now, and each is home to its own unique species—M. boesemani in the lake and M. ajamaruensis in the river. These fishes are each other’s closest relatives in the genus and likely speciated when, at some point in the recent past, the river meandered away.
Knowing the story of a fish—where it is found, when it was found, how it was found—can greatly add to the appeal of keeping it in captivity. Boeseman’s Rainbowfish is a dazzling and hugely popular species, but few know of its enigmatic sister species and the lengths researchers went to rediscover it in the wild. For those aquarists looking to add something a bit unusual, the Ajamaru Rainbowfish is a fascinating choice which few are likely to be familiar with. Though one can’t help but wonder, if the Ajamaru Rainbowfish is not from Lake Ajamaru, wouldn’t it make more sense to call it the Kaliwensi Rainbowfish?