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For the present paper 35 specimens of sea mullet (Mugil cephalus) from different age groups were investigated. The material was collected between May 2010 - September 2011 along the coast, the main points are two: Varna Bay and the mouth of the river Veleka. The main objective of the study was to establish the food spectrum of mullet, and thus a connection could be made between food components. The methods which were used and defined to study the food spectrum and the relationship between different food components are as follows: frequency of occurrence and dominance index of the nutritional components; the filling index and stomach emptiness index, as well as selectivity coefficient of a meal.Results showed that detritus, zoobenthos (Rissoa sp. and Trochammina inflate - 71.43%) and macrophytes (Cladophoraceae family - 63.64%) dominated in stomachs. Several potential toxic species were also found: Amphora coffeaeformis, Pseudo-nitzschia delicatissima, Pseudo-nitzschia seriata, Prorocentrum cordatum, E. pyriformis, P. minimum, Protoperidinium crassipes. The results for the frequency of occurrence (pF) showed that the most common in the stomach of a mullet of the macrophytes are the species of family Ulvaceae - 45.5% ; family Cladophoraceae - 45.5% ; of phytoplankton - Navicula spp (109,09%).; of zoobenthos: Nematoda g.sp. - 42.9% and Trochammina inflate - 28.6 %. The low emptiness index (0.0857) defines the grey mullet as an often eating fish. The small fish reaching up to 3-4 cm eat phytoplankton and zooplankton. Until now, research on the food spectrum of sea mullet by the Bulgarian sector of the Black Sea have not been conducted. [ABSTRACT FROM AUTHOR]