Explain how fish gills have such a high surface area. Fish gills contain highly flattened structures that increase the surface area, heiping gases and nutrients move across them. The surfaces of the gills are highly folded, making an extensive surface for gas exchange. Fish gills consist of a highly branched network of tubelike structures. This increases the surface area for gas exchange. The gills are highly perforated to allow for easy flow through while the fish is swimming..