Nomenclature and Taxonomy

At the risk of channeling my inner Juan Miguel, the nomenclature of the dwarf gourami is worth discussing. The dwarf gourami was originally described in 1822 as Trichopodus lalius. Later, the genera Trichopodus and Trichogaster were merged, and the dwarf gourami was placed in Trichogaster.

Still later, taxonomists recognized Colisa as the appropriate genus for the smaller gouramis, where the dwarf gourami remained for much of the 20th century as Colisa lalius (more often seen as C. lalia, an error that became the norm). This classification remained largely unchanged until the 1990s and early 2000s, when molecular studies showed that Colisa was not a distinct lineage. The larger gouramis were returned to the resurrected genus Trichopodus, while the smaller gouramis were transferred back to Trichogaster, with Colisa becoming a junior synonym.

A recent study examining the genus Trichogaster questioned the identity of Trichogaster fasciata. The authors were unable to verify the presence of a distinct species corresponding to T. fasciata and suggested that the fish traditionally identified by this name may actually represent the dwarf gourami, T. lalius. This interpretation remains controversial, although some sources have begun applying the name T. fasciata to the dwarf gourami. 

Complicating matters further, the name T. fasciata has historically been associated in the aquarium hobby with the banded gourami, a superficially similar but larger and less vividly colored species. I prefer the name T. bejeus for this fish, reserving T. fasciata as a problematic historical name rather than applying it to the dwarf gourami. In my opinion, the evidence supporting the transfer of the dwarf gourami to T. fasciata remains insufficient. Even if future research demonstrated that fasciata was the correct historical name, the overwhelming and long-standing use of lalius in both scientific and aquarium literature, combined with the potential confusion with the banded gourami, makes a strong case for conserving T. lalius.
 

And if you want to go really far down this particular taxonomic rabbit hole, there is even debate over the grammatical gender of Trichogaster and whether certain species names are adjectives or nouns. These questions help explain why older and newer sources disagree over names such as fasciata, fasciatus, lalius, and lalia: proof that sometimes the hardest part of naming a fish is not identifying the fish at all.