Lake Poso, one of the ancient lakes of Sulawesi, Indonesia, has several endemic fish species, including the ricefishes (Oryzias nigrimas), local name rono pahit. Populations of Poso Lake endemic species are declining, due to the introduction of alien species, lakeshore development and watershed land-use changes. One way help maintain an O. nigrimas population is through captive breeding and domestication, for which knowledge of food habits is a pre-requisite. The purpose of this research was to

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... study the food habits of O. nigrimas. The research was conducted during April 2018. Samples were collected from three sampling sites: Watudilana in Pamona Urban Village, Tolambo Village and Taipa Village. The Index of Preponderance (IP) and Relative Length of Gut (RLG) were calculated the results show that O. Nigrimas is an omnivorous-herbivorous fish with an average IP range of 57.73 to 70.75 for vegetable matter and 29.25-42.27 for animal food (prey), while the RGL range 2.48 to 3.26. Rhizosolenia sp. (IP 77.84) was the most dominant plant-based diet component, while unidentified Annelida larvae (IP 24.49) were the most common animal food. KEY WORDS Oryzias, food habits, index of preponderance, Poso Lakes.