Resumo

The red seaweed Asparagopsis armata synthesizes bioactive secondary metabolites with in vitro antibacterial activity. In aquaculture, the fat acid-enriched live feed Brachionus (Rotifera) can be a vector of pathogenic bacteria leading to high fish larvae mortality, especially during the first days of rearing. This study addresses the potential of A. armata-derived metabolite extracts as a novel antimicrobial technology in fish larviculture. In a pilot gilthead seabream (Sparus aurata) larval rearing experiment, live feed were treated for 30 min with (1) lab-made and (2) commercial dehydrated (YSALINE ®100) A. armata extracts prior to their addition to culture tanks. The experiment started at the hatching of gilthead eggs and took 11 days. Bacterial communities in tank water and associated with fish larvae as well as larvae development and survival were monitored. Flow cytometry measurements revealed no differences between the total bacterial load present in water from treatment and control tanks. However, Vibrio spp. counts were significantly lower under the commercial extract treatment (counts below the detectable limit) in comparison with the control (10 to 400 Vibrio CFU/ml water; 150 to 1300 Vibrio CFU/ fish larvae). PCR-DGGE fingerprinting showed that the structure of bacterial communities in tank water and fish larvae were clearly distinct from one another, but were not altered through the treatment of live feed with A. armata-derived metabolites. Higher survival rate and total dry weight of fish larvae were registered under the commercial extract treatment in comparison with the lab-made extract treatment and the control. These results suggest that the application of algal-derived metabolites might enhance fish larvae survival in aquaculture tanks through the selective suppression of potentially pathogenic bacteria (e.g. Vibrio spp.), encouraging further research on the effects of 'YSALINE ®100' at longer rearing periods and larger production scales.