The origin, evolution and pattern of freshwater fish in China

my country has a vast territory and is located in the southeastern part of the Palearctic zoogeographic zone and the northern part of the Oriental zoogeographic zone. It is the only country that spans two major regions among the six major zoogeographic zones in the world. Our country is located at the southeastern end of the Eurasian continent and has an ancient geological history. Some major events in the earth's geological history, such as the collision of the Indian plate and the Eurasian plate, and the uplift of the Tibetan Plateau, are directly related to our country. These characteristics of fauna and geography make my country and its surrounding areas one of the important key areas for establishing the theory of world fauna evolution and historical biogeography.

The study of Chinese fossil fish shows that in the Eocene epoch, the main genera and species were extinct, and some subfamilies had emerged; by the Miocene epoch, many living genera had appeared; by the Pliocene epoch , the fish fauna is very close to the existing fish fauna. At the same time, in the Eocene, there were differences between the north and the south in China's fish fauna. There are two hypotheses in historical biogeography to explain the different endemic distributions of different local biological species, namely the diffusion hypothesis (dispersal) and the isolation and differentiation hypothesis (vicariance). The diffusion hypothesis holds that organisms originate from a certain place and then spread across barriers to other areas, thus forming a discontinuous distribution pattern. The view of isolation and differentiation holds that organisms first formed a wide distribution in these places, and then barriers appeared in the middle to separate them into discontinuous distribution. Until the mid-20th century, the resurrection of the continental drift theory and the proposal of the Ban Kuai theory verified the isolation and differentiation hypothesis, and pan-biogeography centered on the isolation and differentiation hypothesis also received attention. Pan-biogeography believes that drawing the distribution range of organisms on a map becomes a trajectory. The trajectories of different groups may overlap to form a universal trajectory. The most common trajectory will reflect some common geological event. Therefore, the characteristic of modern biogeography is to study the occurrence of geological events through the geographical distribution of organisms, and to explain the formation process of biogeographic distribution patterns through geological events.

China's freshwater fish belongs to the East Asian freshwater fish fauna. It is a unique freshwater fish group in East Asia that was formed in East Asia during the uplift of the Tibetan Plateau in the late Tertiary Period, especially the early Quaternary Period. It appeared relatively late in geological history, and its geographical distribution is limited to East Asia, that is, the area east of the Tibetan Plateau and the Red River, including China, Japan, the Korean Peninsula, and the Russian Far East.

The Himalayan orogeny from the late Tertiary to the early Quaternary period and the global climate cooling in the late Tertiary period caused changes in the cold, hot, dry, wet climate and vegetation. During the Ice Age, sea levels dropped, and the eastern and southern parts of mainland China were connected to many islands in the western Pacific many times, causing migration and distribution changes of terrestrial animals. Due to the Himalayan orogeny and global climate cooling, there has been an important impact on East Asian freshwater fishes. During the Quaternary Ice Age, species as a whole retreated southward, and fish fauna exchanges occurred in different water systems. During the interglacial period, different species spread northward, resulting in the existence of widespread species and relict species. Changes in glacial and interglacial periods also caused the exchange of fish fauna among large rivers such as the Yangtze River and tributaries in the upper, middle and lower reaches of the rivers, and also contributed to the occurrence of species differentiation events in the upper, middle and lower reaches. The differentiation of fauna in southern and northern my country is greater in the north and smaller in the south. In the northern region, due to the drop in temperature, some fish adapted to cold water have emerged, such as fish from the subfamily Yarrowinae and the subfamily Aminoideae. At the same time, salmon and trout have spread from the extreme north to the south. On the other hand, due to the uplift of the Qinghai-Tibet Plateau, the landforms around the plateau have undergone intense cutting, with narrow valleys, steep gradients, and large river drops, forming a rapids environment, which has produced the subfamily Loachidae, the family Loachidae, and the family Diploidae. , Brachycephalidae and other fish adapted to the rapid environment. After the Qinghai-Tibet Plateau rose sharply, it formed a special plateau alpine environment, producing cold-loving indigenous species in the plateau and mountains, such as Schizothorax subfamily and Loach subfamily. At the same time as the Qinghai-Tibet Plateau rose, a large-scale alluvial plain developed in eastern my country. Under the influence of the East Asian monsoon, river water levels changed significantly seasonally, resulting in special habitats such as the middle and lower reaches of the Yangtze River where large rivers and lakes are interconnected. It comes from fishes such as the subfamily Silver Carp, the subfamily Sophia, the subfamily Sodium, the subfamily Sophia, and the subfamily Sophia.

According to the geographical distribution of fossils and living fish, it can be seen that there are differences between north and south in the origin and evolution of freshwater fish in East Asia. There are two differentiation centers, and different groups are continuously differentiated in these two differentiation centers. In the differentiated grid, there are extensive exchanges between the northern and southern fauna, and the existence of widespread types reduces the differences between the north and the south. At the same time, different new groups evolved in the center of north-south differentiation, continuing to retain the existence of differences between north and south. Generally speaking, the origins of the subfamilies Plionidae and Plutoninae may be in the northern differentiation center, but most of the extant species diverged in the southern differentiation center. Loach subfamily and subfamily Loach subfamily have differentiated into unique species in the southern and northern differentiation centers. The mixed zone of the two major flora is in the middle and lower reaches of the Yellow River and Yangtze River basins. This area has a large number of the most eye-catching specialty fish species of our country.

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