<p>Despite its abundant protein content, mustard seed remains underutilized as a food source due to its high concentration of glucosinolates and various anti-nutritional factors. While glucosinolates and their degradation products demonstrate potential as deterrents against insect pests, they also restrict the use of mustard seed in both human food and animal feed. Mustard is globally cultivated for oil extraction from its seeds, with seed meals remaining as byproducts after oil extraction. The protein content of these seed meals, commonly referred to as oil cakes, is comparatively higher (32–38%) than that of sesame (17%), flax (16–18%), and chia seeds (16–18%). However, the presence of anti-nutritional factors limits their use, restricting their agricultural application primarily to animal feed ingredients. The relationship between anti-nutritional factors and their applications is inversely proportional: higher concentrations limit their use in feed but enhance their potential as insect pest deterrents. Analytical techniques, including spectrophotometry, titrimetry, High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS), can be used to quantify anti-nutritional factors for determining appropriate feed practices. This review provides a comprehensive overview of the phytochemical composition of seeds and seed meals from brown, black, and white mustard, emphasizing their biological functions in fish feeding and economic relevance in insect pest reduction. The findings reveal that strategic processing can optimize the dual-purpose application of mustard seed meals, simultaneously reducing anti-nutritional factors for enhanced feed value while preserving bioactive compounds for sustainable pest management. This integrated approach effectively maximizes economic value from agricultural byproducts.</p>