In order to determine the diet of Nannothrissa stewarti in Lake Mai Ndombe, 667 specimens with total length between 9.0 and 49.84 mm were studied. These fish were sampled by active fishing during the 24 h cycle between September 2018 and October 2021. The vacuity (%) and intestinal coefficients were 38.71% and 0.69 ± 0.03, respectively, classifying N. stewarti as invertivorous. The calculated feeding indices showed that zooplankton are the essential prey (%Ffi = 88.8; %IP = 90.0; and %IRI = 90.8) while phytoplankton are the incidential prey. Larvae feed on cyclopoid, copepods, and nauplius while adults consume cladoceras, copepods, rotifers and phytoplankton. This fish begins its feeding activity early in the morning (5:00 am), his stomach fills up around 1:00 pm and empties completely around 1:00 am. Thus, N. stewarti in various steps growing ages both males and females are zooplanktons feeders.
Key words: Lake Mai-Ndombe, Nannothrissa stewarti, food indices, diurnal.
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