The Celebes Rainbowfish (Marosatherina ladigesi)

In the southwestern tip of Sulawesi (formerly known as Celebes) lies the Karst Maros, the world’s second largest karst formation, full of towering limestone cliffs, crystal clear lowland streams and a highly unique fauna found only in this small corner of the world. It’s here that we find the natural population for one of the aquarium trade’s most beautiful and popular species of freshwater fish—the Celebes Rainbowfish (Marosatherina ladigesi).

Its common name is a bit of a misnomer, as the true rainbowfishes of the Family Melanotaeniidae, which are found only in Australia and New Guinea, are only a distant relative of the this fish. Instead, it belongs to an entirely separate family (Telmatherindae, known commonly as the “sailfin silversides”) that is restricted mostly to Sulawesi. These two groups are estimated to have split more than 40 million years ago, with the closest relative of Marosatherina being another popular group of small and colorful aquarium fishes—the blue-eyes of the family Pseudomugilidae.

Adding to the confusion, most aquarium sources still list this species under an older scientific name, Telmatherina, which is now used only for a group of fishes found further east in the Malili Lakes of Sulawesi. In fact, Marosatherina—a group named after the Maros Karst where it is found and which M. ladigesi is the only member of—is now thought to be a fairly distant relative of Telmatherina and likely colonized Sulawesi on a separate occasion via marine dispersal. We can find evidence for this saltwater tolerance in the ability of the Celebes Rainbowfish to be successfully kept in brackish water aquariums, even though the wild population is said to only be found in fully freshwater streams and estuaries.

Obviously, this is one fish that can live in a wide range of water conditions, but, whether kept in freshwater or at low salinity, it is important to avoid keeping M. ladigesi at an acidic pH. The limestone landscape that this species calls home naturally leads to alkaline water parameters, and, if not replicated in captivity, this can oftentimes lead to long-term health issues. This is especially true if attempting to breed this fish. As a shoaling species, it is recommended to keep the Celebes Rainbowfish in small groups with a relatively even number of males and females. The sexes can be reliably told apart based on the larger and morecolorful dorsal and anal fins of the male, which will regularly display their flamboyant finnage in an effort to impress any females and to ward off rival males. Eggs are scattered in vegetation (Java Moss being an excellent choice for this) and the young can be grown in a separate aquarium using commercially available fry foods.

Feeding M. ladigesi poses little problem, as most any dry or frozen food for carnivores will be readily accepted. An appropriate aquarium setup should be densely planted to replicate the sluggish Sulawesi streams this species inhabits. Possible tankmates for a Southeast Asian freshwater biotope might include glassfishes, ricefishes, halfbeaks and blueeyes, all of which will thrive in hard water conditions. Similarly, most livebearers (e.g. guppies, mollies, platies, swordtails) will also do well, as will some of the more peaceful smaller cichlids from the African rift lakes.