The large (around 60 cm) spiny eel Mastacembelus unicolor was scientifically recorded early on. The two researchers Kuhl and van Hasselt discovered it in the western part of Java during their stay there from 1820 to 1823 and also made a drawing of the animal. The two paid for their thirst for knowledge with their lives, dying of tropical diseases in 1821 (Kuhl) at the age of 24 and in 1823 (van Hasselt) at the age of 26. Their records and collected specimens were later used by other scientists as the basis for species descriptions. Cuvier described Mastacembelus unicolor on this basis in 1832.
M. unicolor remained completely unknown in aquariums for a long time, although the species is widespread in Indonesia but apparently not common anywhere. We first received two adult specimens of the species by chance in 2018 (see https://www.aquariumglaser.de/en/22-spiny-eels/mastacembelus-unicolor-2/) and in 2024 in a younger specimen measuring 20-25 cm in length (https://www.aquariumglaser.de/en/fisharchive/mastacembelus-unicolor-4/). Now, for the first time, we have managed to import a slightly larger number of juvenile animals (10-20 cm in length). The conclusion from this is that juveniles differ greatly in color from sexually mature specimens. The species-typical snow-white stripe at the edge of the dorsal, caudal, and anal fins only develops from a length of about 20 cm; fortunately, this color change can be observed in all transitions in our current import. And we learn something else from this import: there are two color phases in young M. unicolor, one more reddish and one blackish-brown.
Once again, this shows how valuable wild-caught imports are for gaining knowledge, especially of fish species that, due to their characteristics (in this case, their achievable final size), are only of interest to a few specialists as aquarium fish.
For our customers: the animals have code 426722 on our stock list. Please note that we only supply wholesalers.
Text & photos: Frank Schäfer
