Given that the main sources of food for aquaculture are fishmeal and oil, which is not sustainable in the long run, the nutritional potential of alternative sources such as plants and insects is being intensively explored. In this study, five experimental diets of juvenile sea bass Dicentrarchus labrax were tested with different proportions and origins of plant/animal meals, in addition to the commercial diet. Two were negative (CVEG) and positive control (CFISH) and contained a high proportion of vegetable and fish proteins and oils, respectively. Other diets contained the majority of plant proteins with the addition of insect protein from Hermetia illucens (CVEG+HM), a combination of plant proteins, by-products from the poultry industry and insect meal (CVEG+PBM+HM) and a diet with high proportion of fish protein and oil and insect meal (CFISH+HM). After 125 days of the feeding trial, the group fed commercial diet demonstrated largest increase in length (49.11%) and weight (85.95%), while the smallest increase in length (42.2%) and weight (80.41 %) was recorded for the CVEG group. The CFISH group had similar growth to the control group. The highest value of the condition index was recorded for CFISH+HM (1.28 ± 0.01). The CFISH group had the best food conversion index (0.97 ± 0.02), lowest fecal energy value (234.54 ± 7.12 kcal), i.e. the highest food utilization rate, and the highest total lipid content in fillets. Experimental groups fed diets with a higher content of omega-3 and -6 fatty acids originating from insect meal or rapeseed and flaxseed oil respectively (CFISH+HM and CVEG) demonstrated a higher content of these acids in sea bass fillets. The results underline the importance of fish meals in the diet of juvenile sea bass and alternative sources of dietary protein and oil cannot meet the demands of fish at this developmental stage.