One of the most important natural ecosystems in the world is peat-land. It comprises a unique and complex ecosystem, which has a globally important role in biodiversity conservation at genetic, species and ecosystem levels and contains many species found only or mainly in peat-lands. These species are adapted to the special acidic, nutrient poor and waterlogged conditions. Peat swamp ecosystems are considered one of the most threatened, neglected, and poorly understood biotopes and their importance is underappreciated. The race to catalogue biodiversity before it disappears is particularly intense in the peat swamps. Most of fish biodiversity research in peat swamp systems relies on morphological diagnosis, primarily of adults and relatively large fish which can be morphologically distinguished. Despite the prevalence of planktonic larvae in tropical peat swamp systems, comprehensive larval identification keys for these systems are extremely limited making it almost impossible to identify larval specimens solely by their external appearance. In addition, in their early life, the morphology of a species can change quickly and significantly during its development from pre-flexion larvae to postflexion to the pre-juvenile stage. Thus, the same species at different developmental stages may be identified differently when based on morphological characteristics.