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In Europe, intensive aquaculture began at the end of the 19th century, when governments decided to breed fish to obtain fingerlings which were used to restock lakes and rivers (Polanco & Bjorndal 2018). Those fish represented an important source of protein for river communities, and helped to alleviate hunger. Efforts were made to promote the most appreciated species, such as salmonids, which are carnivorous. As production increased and fish were kept under intensive care for longer periods, farmers began to formulate feeds. In the beginning they captured macroinvertebrates in nearby water bodies, but that was seasonal and in limited supply. Later, fish were fed using waste products from slaughterhouses, which were chopped up into small pieces and thrown in the water directly. As a result, many salmon farms were established close to slaughterhouses.
Fish farms near ports used discarded fish from the fisheries but the supply was not always constant and was more difficult to organize as production increased. So farmers began making a paste with discarded fish that was blended together to make fish meal, to which they sometimes added plant protein. The paste could also be shaped into pellets, which facilitated spreading over many tanks, but since it was quite humid it could not be kept for very long periods before going bad. As time went on, fish nutritionists started to develop granulated feeds around the middle of 20th century. They were drier and were easier to formulate to the nutritional requirements of each species, and were much easier and cheaper to store.
Those first granulated or compound dry feeds facilitated the expansion of fish farms. Since then there has been intense research on the most appropriate and economically profitable raw materials to use in feed formulas. The whole process was improved by introducing the technique of extrusion, which applies high pressure to the feed paste during short intervals, increasing the temperature, making the granule lighter (allowing it to float in the water for longer periods) and allowing the incorporation of more fish oil. It also improved the compactness of the granules so that they did not dissolve immediately upon contact with water.
More recently efforts have been made to produce feeds that are more sustainable and organic. As mentioned above, for carnivores that means reducing the amount of fish meal in fish feed (and replacing it with plant protein like soya meal) and fish oil. For tilapia is also means reducing or eliminating any fish meal or fish oil, while maintain flesh quality. Recent research has focused on alternative protein sources for many types of fish, including the use of algae or insect meal.
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