The Archipelago hosts very diverse and biogeographically unique fish communities. About 735 fish species in 109 families have been recorded from the Archipelago to date. Abundances and species diversity increase in East-West and South-North direction and the highest diversity at individual sites are found at Abd al-Kuri. Abundance-Frequency-Distributions and Occurrence- Frequency-Distributions reveal that many species have relatively small populations and occur at few sites only. Modelling of the archipelagic diversity of fish using incidence-based richness estimators such as Chao2, ICE, or Jacknife2 indicate that the actual diversity ranges between 830 and 890 species (excluding deep-dwelling species below 200 m depth). The islands are thus endowed with the highest diversity of marine fishes in the Arabian region and match up with other tropical island groups or even countries in the Indian Ocean. The diversity is especially striking in comparing Species-Area-Relationships across the surrounding eco-regions. For example, certain "reef" associated families and functional groups are as diverse, or even more diverse, than their respective groups in the entire Red Sea, even though the islands' coastline is approximately eight times less in length and supports considerably fewer biogenic reefs. Thus, other ecological determinants than the species-area relationship such as habitat heterogeneity, niche diversity, biogeographic nesting and productivity are more likely key factors. The impressive fish diversity is, for example, matched by high fish biomass productivity, with certain sites ranking among the most productive sites in the Indian Ocean, and the interplay between these parameters is currently a major line of our research. The Archipelago may thus well be considered a marine "micro continent" in terms of its ecological ichthyogeography.