years, about 90 percent of the native fish species in the lake were haplochromines. Disregarding the haplochromines, the only native Victoria cichlids are two critically endangered tilapia, the Singida tilapia or ngege (Oreochromis esculentus) and Victoria tilapia (O. variabilis). In 1927–1928 Michael Graham conducted the first ever systematic Fisheries Survey of Lake Victoria. In his official report of the expedition, Graham wrote that "The ngege or satu Tilapia esculenta, is the most important food fish of the lake, whether for native or non-native consumption. No other fish equals it in the quality of the flesh. It is convenient size for trade, travels well and is found in much greater numbers than other important fish, such as semutundu (Luganda), Bagrus sp.". Furthermore, Graham noted that the introduction of the European flax gill net of 5 inch mesh had undoubtedly caused a diminution in the number of ngege in those parts of the Kavirondo Gulf, the northern shore of the lake, the Sesse Islands and Smith's Sound which are conveniently situated close to markets. Survey catches in 1927–28 included several Haplochromis species that are now thought to be extinct, including: Haplochromis flavipinnis, Haplochromis gowersii, Haplochromis longirostris, Haplochromis macrognathus, Haplochromis michaeli, Haplochromis nigrescens, Haplochromis prognathus. As well as being due to the introduction of Nile Perch, the extinction of cichlids in the genus Haplochromis has also been blamed on the lake's eutrophication. The fertility of tropical waters depends on the rate at which nutrients can be brought into solution. The influent rivers of Lake Victoria provide few nutrients to the lake in relation to its size. Because of this, most of Lake Victoria's nutrients are thought to be locked up in lake-bottom deposits. By itself, this vegetative matter decays slowly. Animal flesh decays considerably faster, however, so the fertility of the lake is dependent on the rate at which these nutrients can be taken up by fish and other organisms. There is little doubt that Haplochromis played an important role in returning detritus and plankton back into solution. With some 80 percent of Haplochromis species feeding off detritus, and equally capable of feeding off one another, they represented a tight, internal recycling system, moving nutrients and biomass both vertically and horizontally through the water column, and even out of the lake via predation by humans and terrestrial animals. The removal of Haplochromis, however, may have contributed to the increasing frequency of algal blooms,