Sungai Merbok Mangrove Forest Reserve, encompassing the Merbok river estuary, was established as a permanent forest reserve in 1951 and is the second-largest intact mangrove forest patch in Peninsular Malaysia. Despite its importance, few studies have been conducted to assess its aquatic biodiversity. In this study, we surveyed the fish diversity of the Merbok river estuary, and its adjacent marine waters. We recorded 138 fish species belonging to two classes, 18 orders, 47 families, and 94 genera. The richest order is Perciformes, with 32 recorded species, represents 23% of the alpha diversity, followed by Carangiformes with 21 recorded species or 14% of the diversity. Low taxonomic diversity overlaps with previous inventories and indicates that the inventory is still incomplete. All specimens examined are catalogued and deposited in a local museum collection. The fish checklist presented here represents a step forward in the conservation of fish diversity in the Merbok river estuary.

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