Li Sizhong (Chinese: 李思忠; Wade–Giles: Li Sze-Chung; 2/19 1921 – 1/11, 2009) was an ichthyologist with the Institute of Zoology (中国科学院动物研究所) at the Chinese Academy of Sciences. Throughout his research career, he made numerous discoveries of new fish species (or subspecies), and published many books and research papers describing the fauna and geographical distribution of fishes in China and beyond. He translated and helped publication of the Chinese editions of Fishes of the World (2nd edition, by Joseph S. Nelson) and Fish Migration (a popular science book by Russian zoologist Peter Y. Schmidt). Li was the major author of two published volumes in the Fauna Sinica monograph series, systematically reviewing and describing orders of bony fishes that include flat fish, cod, silverside, pearlfish, killifish, flying fish, etc. in or near China. He had written over 40 popular science articles about fish on Chinese newspapers and magazines, and been responsible for compiling and editing fish-related entries in several standard reference books (including Encyclopedia of China).
Starting from the early 1950s, Li helped to initiate and participated in China's systematic surveys of marine fishes in Bohai Sea, Yellow Sea and South China Sea, along China's coast. His scientific career, however, was interrupted in 1957 when he was labelled a "rightist" during the Anti-Rightist Movement. From then until the mid-1970s, while his research and publication capacity had been severely impacted by whims of political campaigns and turmoils, he managed to conduct surveys of freshwater fishes in the Yellow River, Ou River and Ling River, as well as in interior regions such as Xinjiang and Gansu provinces. Only until after the Cultural Revolution, he was able to resume normal research activities.
In his book Studies on zoogeographical divisions for fresh water fishes of China, Li divided the fauna of freshwater fishes in China into five major regions based on characteristics of fish species distributions, geographic environments and geological histories of these regions. According to his method, the demarcation line between Holarctic and Indomalaya regions in China, as far as freshwater fishes are concerned, lies largely along the Himalayas and Nanling Mountains ranges. This contrasts with the prevalent view of demarcation line between Holarctic and Indomalaya regions along the Qinling Mountains, even though the latter does not extend into Eastern part of China. Freshwater Ecoregions of the World (FEOW), a collaborative global biodiversity project partly sponsored by World Wide Fund for Nature (WWF), cites this book as a source of references in delineation of freshwater ecoregions of China.
Two of his books are published posthumously. In Fishes of the Yellow River and Beyond, he described over 170 native fish species and the characteristics of fish distribution in the Yellow River and its tributaries; a collection of his papers and popular science articles, as well as a personal memoir, are also included in the posthumously-published book. Another volume of the Fauna Sinica series which he worked on during his last years, covering fish species in China within the orders of Beryciformes, Zeiformes, Lampriformes, Gasterosteiformes, Mugiliformes and Synbranchiformes, is yet to be published.