Climate change has become a significant driver of change in marine environments, affecting fish populations, biodiversity, and ecosystem dynamics globally. Rising ocean temperatures, acidification, sea level rise, and deoxygenation are altering species distribution, breeding cycles, and food web structures. This paper analyzes the multifaceted impacts of climate change on fish populations and marine ecosystems. It also discusses the socio-economic implications and explores adaptive strategies for conservation and sustainable management. With marine resources critical for global food security and livelihoods, urgent coordinated action is required to build climate-resilient oceans.