In some species, the gills of air-breathing fishes are so small that only 20% of the oxygen is obtained through the gills.
(the gills of air-breathing fishes; are; so small that only 20% of the oxygen is obtained through the gills; L:In some species) (only 20% of the oxygen; is obtained; )
the gills of air-breathing fishes only 20% of the oxygen
are is obtained
so small that only 20% of the oxygen is obtained through the gills L:In some species