The Lempuk fish (Gobiopterus spp.) is a kind of fish that is exclusively found and inhabits the Ranu Grati area in Pasuruan Regency. The Lempuk fish is a prominent tourist attraction and is frequently targeted for fishing due to its significant economic significance. This leads to excessive exploitation, resulting in population decline and posing a threat to its sustainability. Therefore, it is necessary to identify the abundance and type of plankton, as well as its relationship with the study of stomach contents, to gather supporting data for future domestication efforts. The sampling was conducted three times, with a two-week gap, at five distinct sites. The research employed a quantitative-descriptive approach and the sampling a purposive sample technique. The research findings revealed the presence of four distinct classes with 20 different species in the phytoplankton community, as well as four distinct classes with 12 genera in the zooplankton community. The study of stomach conten this fish shows, primary diet of this fish, as shown by their propenderence index, consists of phytoplankton from the Asterionella species and zooplankton from the Daphnia genus