FRESHWATER FISH OF MALAYSIAN BORNEO

This chapter focuses on taxonomic richness of freshwater fish of Malaysian Borneo include endemism, research status, conservation effort, and investment needs. Freshwater ecosystems in Borneo support one of Southeast Asia’s most distinctive fish assemblages, influenced by ancient geology, diverse habitats, and long-term river isolation. In Sarawak and Sabah, over 300 valid freshwater fish species are recorded, with high species richness from the order Cypriniformes, Siluriformes, Anabantiformes, and Gobiiformes. Endemism is a defining feature, with many lineages occur in only a single basin or habitat, particularly peat swamps and highland headwater streams, and most members of the family Gastromyzontidae occur nowhere else. The earliest freshwater fish collections from Borneo date to the 1820s, and the number of species described from the island has since increased from just over a hundred to more than 400 today, driven by a steady rise in new species descriptions over the past decade. Yet major gaps persist, as peat swamps remain undersampled, upper watersheds lack long-term datasets, and many historical type localities have been altered by land-use change. The continual discovery of new taxa indicates that true species richness is still underestimated and reinforces the importance of integrative taxonomy that combines morphology, genetics, and ecological data. Conservation needs are urgent as freshwater habitats are threatened by land conversion, river modification, invasive species, and habitat impoundment. Peat swamps are particularly threatened, which affects narrow-ranged species such as Paedocypris micromegethes, and Betta chini. Ongoing efforts involve protected areas, riparian buffers, captive breeding and community-managed Tagang systems, however implementation has not been consistent in the region. To improve the conservation of freshwater fish in the future, basin-wide biodiversity surveys and updated Red List assessments are needed, as well as the identification and protection of important peat swamp habitats, headwater streams, molecular reference libraries for eDNA and building capacity with local researchers and communities. In the future, trans-border co-operation with Kalimantan will also increase knowledge of inter- watershed connectivity. Malaysian Borneo retains its worldwide superlative for freshwater fish diversity, and the conservation of this part of natural heritage requires science integration, sound management, and continued commitment.
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DR. JONGKAR GRINANG

Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak

Jongkar Grinang is a taxonomist specialising in the taxonomy and systematics of freshwater crabs, fish, and macroinvertebrates. He is currently a Research Fellow at IBEC, UNIMAS. His research interests span various fields, including taxonomy and systematics, population ecology, biological indicators, stream ecology, fish acoustics, and conservation biology. Jongkar has authored significant research works that feature species descriptions and ecological studies as well as contributions to book chapters. He has described over 20 new species of Bornean freshwater crabs and fish while actively pursuing regional taxonomy. He also serves as a reviewer and editorial board member for several journals and is affiliated with professional organisations such as the Friends of Sarawak Museum, Malaysian Fisheries Society, British Ecological Society, and the Systematics Association. His combined skills in research methodologies, field surveys, ecological statistics, data interpretation, and applied conservation efforts are instrumental in promoting biodiversity management and environmental planning throughout Malaysian Borneo.