Spirulina platensis is a protein rich cyanobacterium known for its remarkable nutritional profile, comprising essential amino acids, vitamins, minerals and health promoting bioactive compounds such as phycocyanin and carotenoids. These characteristics have led to its extensive use as a functional ingredient in human diets, animal nutrition, and aquaculture feeds. In fisheries, Spirulina enhances growth performance, immunity, reproduction, pigmentation, and overall health of cultured aquatic species. Beyond its nutritional applications, Spirulina platensis has emerged as a promising biotechnological resource due to its content of polyhydroxybutyrate (PHB), a biodegradable and biocompatible polymer. PHB offers potential for the development of sustainable and animal-free capsule shells as an alternative to conventional gelatin-based capsules. This article reviews the composition of Spirulina platensis, its importance in aquaculture, and its emerging role in the pharmaceutical industry as a source of eco-friendly capsule materials.