Oil palm cultivation is expanding especially in Malaysia, where natural land occupied by small streams and rivers has been converted into an agroecosystem. This study assessed and estimated fish species richness and fish diversity in the tropical oil palm plantation in Terengganu, Peninsular Malaysia, along with their importance, and conservation status. From 57 fish species recorded, 28 species were suitable as ornamentals, 21 species for both food and ornamentals, and four species were considered suitable as ornamentals, food, and sport fishing. About 54 fish species were classified in the Least Concern (LC) category while one species each was classified in the Data Deficient (DD) and Not Evaluated (NE) categories. More species can be recorded by increasing the sampling efforts as suggested by Chao 1 species richness estimator. Tributary Sungai Nerus has the highest fish species diversity and species richness, while Sungai Jeneris has the lowest fish species diversity, species richness, and species evenness. Continuous data collection can determine the true fish species richness and fish diversity in the oil palm plantation, which can help to suggest good management schemes to conserve fish fauna in this agroecosystem.