Yellow mealworm (T. molitor) is a safe and sustainable alternative protein source for aquafeed, given advantages such as high protein content and better amino acid profile when compared to alternative plant-protein sources. This chapter provides an overview of the current use of T. molitor as alternative ingredient to fishmeal. It summarises recent reviews on the use of these invertebrates in aquafeeds and their impact on key performance indicators (KPIs) associated with growth performance and feed efficiency, product nutritional quality, as well as their immunomodulatory potential and effect on host gut microbiota.