Final answer:
The Philippines and surrounding areas in the Central Indo-Pacific realm have the greatest diversity of fish, with over 4,000 species.
Step-by-step explanation:
The greatest diversity of fish is seen in the Philippines and surrounding areas, which are referred to as part of the Central Indo-Pacific realm. This region is considered a global hotspot of marine species richness and endemism, supporting over 4,000 species of fish. This diversity is attributed to the region's large shelf area and a variety of marine habitats that serve as a center for the evolutionary radiation of many groups, including fish.