Climate change has emerged as a major driver of ecological disruption in marine environments, profoundly impacting fish populations and ocean ecosystems. Rising sea temperatures, ocean acidification, sea level rise, and deoxygenation are reshaping species distributions, reproduction cycles, food webs, and biodiversity. These environmental changes threaten food security, coastal economies, and the resilience of marine ecosystems globally. This paper examines the mechanisms through which climate change affects fish populations and marine systems, highlights key case studies, and proposes adaptive strategies for sustainable marine resource management in a warming world.