The primary factor driving changes in fish populations is overfishing, exacerbated by habitat degradation and climate change. Unsustainable fishing practices deplete fish stocks faster than they can reproduce, leading to significant declines in population size. Additionally, alterations in water temperature and salinity due to climate change affect fish distribution and reproduction patterns. Overfishing impacts not only target species but also the entire marine ecosystem, as it disrupts the food web and diminishes biodiversity. To address these challenges, sustainable fishing regulations and adaptive management practices are essential for maintaining healthy fish populations and marine ecosystems.