The early-stage extrusion processing was mainly used in food processing industry. Since the nineteen fifties, America had started to use this technology for feed processing field, especially for processing pet food and pretreatment of feed ingredients. Till the nineteen eighties, it has become the fastest developing technique of feed processing industry in the world, and has started to be applied in each sphere of feeding stuff industry, widely used for dry pet foods, some applications for livestock feed and fish feed. With the unceasing development of technology and the continuous rising of people living standard, the growth of aquaculture must follow the principle of producing green food without pollution, bringing significant attention and lots of intensive study on aqua feed production technology. And there is a consensus that adopting extrusion process to make fish feed is the major means to ensure producing high quality and safe aquatic products for human health, which is also a trend for feed industry progress in the future.

Commercial fish feed extrusion process refers to cook the mixture of feed ingredients under high temperature, moisture and high pressure by means of fish feed extruder within short time, whereby the high temperature is a direct result of friction(dry extrusion) or preconditioning and steam injection (wet extrusion). As a technological treatment, extrusion can make it possible to process a variety of fish feed ingredients, such as soybean, corn, rice, peas and raw materials with high water content. According to the moisture content of raw materials treatment, fish feed extrusion process can be divided into two types - dry type extrusion and wet type extrusion.