Complex sentence: Oceans contain about 10,000 times more saltwater than the freshwater in lakes and rivers; yet a disproportionate 41 percent of extant fish species are freshwater, only 58 percent saltwater (the remaining one percent are anadromous).
Split into simpler sentences: Oceans contain about 10,000 times more saltwater than the freshwater in lakes and rivers; yet a disproportionate 41 percent of extant fish species are freshwater. Only 58 percent are saltwater (the remaining one percent are anadromous).