Essential oils from plants are considered potential diet supplements in aquaculture. Supplementing essential oils in the diet of aquatic animals can improve reproductive performance, antioxidant activity, immune response and resistance to pathogens, as well as modulate the intestinal microbiota. In this work, herb essential oils were analyzed with GC-MS regarding their main bioactive components, in order to identify their potential to be used as fish feed additives. The investigated essential oils were derived from rosemary (Rosmarinus officinalis), thyme (Thymus vulgaris), conehead thyme (Thymus capitatus) and garlic (Allium sativum) herbs. The results of the qualitative analysis showed a great concentration of bioactive substances (>40%) in the aforementioned essential oils, which exhibit proven antioxidant, anti-inflammatory and antibacterial activity. Therefore, the implementation of essential oils in fish feed seems only promising, as it could benefit the overall well-being of aquatic animals and contribute to the sustainability of aquaculture industries leading to high quality feed ingredients.