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Cirkulární a dlouhodobě udržitelná výživa ryb
ROY, Koushik
The linear flow of nutrients from aquafeed, feeding fish to excretory products released by the fish if closed by integrating with plants, then the excretory waste does not seem to be a waste, but rather a resource. Whether a nutrient molecule is going in fish (i.e., nutrition) or coming from fish (i.e., excretion) depends a lot on the interactions of management decisions in aquaculture and the biological or physical environment of a feeding fish. If circular-origin feedstuffs are used in future aquaculture or species that are societal discards are integrated into aquaculture, both offer prospects as a nutrition source either for humans (food) or for farmed animals (feed). However, they are not without problems either- nutritionally. On the one hand, the nutritional requirements of raising such new circular origin 'food' may not be well known. On the other hand, the nutritional value of the circular origin 'feed' may not be perfect. Thus, completely integrating everything (feed and food) within an umbrella of 'circularity' would bring their own, completely new challenges. Feeding decisions or nutrition provisioning in aquaculture greatly impact neutralizing nutrient footprint and achieving sustainable production. But in semi-intensive pond aquaculture, the repercussions of feeding decisions and its resultant nutrient footprint are nothing compared to the many times higher positive value of intangible ecosystem services such systems provide. Therefore, the focus for sustainable production in the future should focus more on ecosystem functioning than blindly curbing production intensity and assuming it would make a significant difference in environmental sustainability. By using fish nutrition and excretion knowledge, there are possibilities to manipulate in-vivo systems to maximize nutrient retention efficiency and minimize losses in-situ. If these pieces of knowledge are applied in line with contemporary ecological principles in outdoor semi-intensive aquaculture systems, future adaptation strategies may be intelligently formulated to achieve improved resource use efficiency of a farming system. The entire system (in-vivo and in-situ nutrients pool) must be visualized as a unit, functioning individually but synchronized. The synchronization mechanisms should be targeted for future biomanipulation. The applications of fish nutrition (and excretion) can also be beyond the nutrition (growth and physiology) of farmed animals or emissions (and re-valorization) of nutrients. Knowledge of the digestibility of different nutrients in a wide range of feed ingredients by a particular fish species, and its established digestible nutrient requirement, can help find more precise replacements of finite, unsustainable, and conventionally overexploited or even non-circular resources presently used in aquafeed of a given species. The knowledge of nutrient partitioning (digestibility, metabolic losses), its retention or total loss limits and repercussions on growth and excretion by fish, composition of excreted products itself (suspended losses versus reactive losses) can further make the recycling and re-use of nutrients (in circular food system models like aquaponics) more precise and more efficient. Even using the knowledge, the in-vivo system of fish can be taken advantage of through tailored feed formulation (crude intake levels) that would result in manipulated levels of excreted nutrients in-situ, available to microbial processes or plants.
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