Cursory study has shown that B. collettei has a taste for terrestrial insects, but there hasn't been a great deal of diet-specific research. This is a similarity it shares with congener B. alburnoides, which also eats terrestrial insects.Silva, Cylene & Ferreira, Efrem & de Deus, Cláudia. (2008). Diet of Bryconops alburnoides and B-caudomaculatus (Osteichthyes : Characiformes) in the region affected by Balbina Hydroelectric Dam (Amazon drainage, Brazil). Neotropical Ichthyology. 6. 237-242. 10.1590/S1679-62252008000200011. Other congeners prefer flying insects, such as B. caudomaculatus, which is known to jump out of the water in pursuit of airborne prey.
