Production of Mycosporine-Like Amino Acids from Gracilaria vermiculophylla (Rhodophyta) Cultured Through One Year in an Integrated Multi-trophic Aquaculture (IMTA) System. This study evaluates the production of biomass and mycosporine-like amino acids (MAAs) throughout the year in Gracilaria vermiculophylla (Rhodophyta) collected in Ria de Aveiro (Portugal). The algae were grown in outdoor tanks in seawater with the addition of fishpond effluents under two different water flows (100 and 200 L h-1) in an integrated multi-trophic aquaculture (IMTA) system (tanks 1200 L; 1.5 m2) and different algal densities (3, 5, and 7 kg m-2). MAA content in IMTA seaweeds was significantly affected by the interaction of time and stocking density, but not by the water flow. The highest MAA content was observed in April (about 3.13 mg g-1 DW) followed by May (1.79 mg g-1 DW). Seaweed biomass productivity was higher in May (372.06 g DW m-2 week-1) than in April (353.40 g DW m-2 week-1). Four MAAs were identified by HPLC and electrospray ionization mass spectrometry (ESI-MS) in G. vermiculophylla: Porphyra-334, Shinorine, Palythine and Asterina-330. The highest levels of Porphyra-334 and Shinorine were reached from November to January and the Palythine + Asterina-330 from April to August. Taking into account the average biomass and MAA production of G. vermiculophylla growing in this IMTA system (8.56 g of MAA in 18 m2 culture along 8 months; 35.5% produced in April), a total amount of 71.33 g MAA year-1 could be produced in this system by scaling up to 100 m2. MAAs could be further used as photoprotector and antioxidant compounds in cosmetic products.