Feed input for the animal subsystem is the primary nutrient input into aquaponic systems, but should also provide adequate nutrition for several bacterial populations as well as a plant crop. Dietary crude protein is one of the most expensive macronutrients in fish diets, and the source of nitrogen (N) for other biotic components. H owever, N nutrient flows through aquaponic systems is not well understood. The aim of the present study was to investigate the effect of shrimp feed with different protein concentrations (30%, 35%, or 40%) on water quality and the growth performance of Pacific whiteleg shrimp (Litopenaeus vannamei) and three edible halophytic plants (Atriplex hortensis , Salsola komarovii , and Plantago coronopus ) in biofloc -based marine aquaponics. The experiment was conducted for 12 weeks, the plants were harvested and seedlings transplanted every 4 weeks. Protein content did not influence shrimp growth in the current study, indicating that feeds with lower protein concentrations can be used in biofloc-based marine aquaponic systems. During the early and mid-stages of cultivation, plants grew better when supplied diets with higher protein concentration, whereas no differences were observed for later harvests. Hence, for maximum production, we recommend providing a higher protein concentration feed in the early stages of system start-up, and switching to a lower protein con centration feed in later stages of cultivation.
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