With implications that go well beyond human health, microplastic contamination in pet foods and fish meals is becoming a crucial yet underappreciated aspect of the worldwide plastic pollution disaster. Microplastics from fisheries, aquaculture, and environmental runoff may find their way into the diets of companion animals and farmed species as commercial feeds increasingly contain marine-derived components. These particles, together with accompanying chemical additives and adsorbed contaminants, cause hazards ranging from gastrointestinal discomfort to oxidative stress and metabolic disturbance in animals. Moreover, contaminated fish meals used in aquaculture and animal feed can transmit microplastics into larger food webs, thereby altering ecological balance and food safety. The longevity of these particles through trophic transfer raises questions regarding long-term ecological stability and possible feedback loops influencing biodiversity and production. Despite rising scientific interest, considerable gaps exist in detection methodologies, regulatory frameworks, and risk assessment processes for microplastics in animal diets. This chapter synthesises existing evidence on microplastic occurrence in pet foods and fish meals, examines biological and ecological repercussions, and underlines the larger implications for environmental sustainability, animal welfare, and food system resilience. Addressing these difficulties needs coordinated monitoring, improved feed processing, and evidence-based regulations to reduce this rising hazard.