## 2 New Trends in Aquaculture Feed Production
### Extraction of Active Ingredients from Molluscs and Algae  
The extraction of active ingredients from plant and animal products is a rapidly evolving research area [43]. From 2000 to 2020, the production of algae and molluscs doubled. In 2020, the production of algae and bivalve molluscs represented 43% of the total aquaculture sector by volume and 7.6% by edible weight [1]. Since 2000, the cultivation of algae (especially macroalgae) has increased steadily [44]. Global aquatic plant production tripled from 10 MT of wet biomass in 2000 to over 32 MT in 2020. A total of 31-38% of 32 MT of algae production is used by humans (99% in Asia) [1]. In 2020, macroalgae production was 4.6 MT. Many algae are used in the food industry as an additive for the production of nutraceuticals (source of polysaccharides), pharmaceuticals, cosmetics (source of hydrocolloids), and fertilisers and feed ingredients. Recently, fucoxanthin, a potent anti-inflammatory, has been extracted from some brown algae [45]. The production of microalgae such as _Spirulina_ spp., _Chorella_ spp., _Haematococcus pluvialis_, and _Nammochloropsis_ spp. is highly developed in some countries [46]. In 2020, the world production of microalgae amounted to 130,000 t. In 2020, the demand for dried microalgae in Italy was 200 t. Meal obtained from algae can be used in fish diets [46]. Generally, the nutritive value of brown algae is lower than that of red and green algae due to the lower protein content. The algae production process can be improved by means of a \"biorefinery\" approach. In this method, active ingredients from the algae are produced using large photobioreactors and are then extracted sequentially, thereby reducing waste, energy inputs, and environmental damage. New technological advances allow algae to be grown on a large scale in coastal and offshore locations. Disease prevention and management and optimisation of environmental parameters during the cultivation phase (nutrients, light, and temperature) are some of the aspects that are still under development. In intensive plants, bacterial and viral diseases are particularly frequent, and disease management costs can represent up to 50% of variable costs. New varieties are needed to improve production and profitability to improve yield, disease resistance, and nutritional characteristics. Microalgae can replace fishmeal and fish oil in fish feeds. However, some technical, biological, and economic difficulties related to the production of high-quality microalgal biomass limits its practical use. According to some recent studies, a level of macroalgae inclusion with rates >10% results in adverse effects on trout growth. Some bacteria and yeasts have a high potential as alternative sources of protein. However, their use is still limited due to high production costs.  
Shellfish production includes approximately 65 species, mainly bivalves (clams (_Venerupis decassata_), oysters (_Ostra Elulis_), scallops (_Pacent jacobaeus_), abalone (_Haliotis Linnaeus_), and mussels (_Mytius galloprovincialis_). Bivalve mollusc farming does not require the use of feed. The active ingredients extracted from molluscs are used in various sectors, such as the production of fertilisers, building materials, pharmaceuticals, and nutraceuticals [47].