Title: Growth trial in Atlantic salmon (Salmo salar) testing six fishmeals in RAS.

Cuba, the largest island in the Caribbean, relied on capture fisheries for marine products until the 1980s, since then they have declined owing to various causes, including natural disasters such as hurricanes. The lack of seafood in the Cuban diet is the main reason why one of the government's current goals is to develop mariculture. To achieve this goal, Cuba has received funding and support from foreign institutions and international collaborations. One collaboration is between the Cuban Fisheries Research Center (CIP) and the Institute of Marine Research (IMR) from Norway, which has been sustained for over 20 years. The most recent stage of this collaboration resulted in the installation of a Recirculation Aquaculture System (RAS) at the Mariculture Experimental Station of Mariel, owned by CIP. The aim of this facility is to create broodstock and produce marine fingerlings in Cuba. Given that the management and initiation of RAS require qualified personnel, the outcome of the present study is to become a training tool for Cuban aquaculture workers. The present study was conducted within a RAS at the Matís Aquaculture Research Station (MARS) in Iceland, and its main objective was to compare performance parameters between six fishmeal treatments for Atlantic salmon. The experiment lasted 56 days, during which water quality parameters were measured daily, and the fish were weighed at the beginning and end of the experiment, which was used to calculate the Specific Growth Rate (SGR). Uneaten feed was collected daily to calculate the feed intake and feed conversion ratio (FCR). In addition, water samples were collected from the biofilter at three time points during the experiment to evaluate the variation in the biofilter community. FCR (0.83-0.87) and SGR (0.96-1.06) showed no significant difference between the six tested feeds during the trial. Statistical analyses based on the diversity of the sequenced DNA extracted from the samples did not reveal significant differences in community diversity. Nitrosomonas Genus, Alphaproteobacteria, and Gammaproteobacteria Class were present in all the water samples. In the end, all feed behaved similarly, and the biofilter function was not affected by the overfeeding process, guaranteeing water quality during the trial.