The potential of Asparagopsis armata to control the bacterial load associated to live feed to improve Seabream (Sparus aurata) larvae performance

Dissertação de mestrado, Aquacultura e Pescas, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2014

Seaweeds are a source of bioactive compounds producing a large variety of metabolites with a broad spectrum of biological activities. This work attempted to understand the use of A. armata metabolites in larval rearing of Sparus aurata, assessing its development and larval quality, by reducing the bacterial load associated with the live feed. Two A. armata products (a laboratory made extract and a commercial powder, Ysaline®100 - YSA) were tested in Brachionus spp. and Artemia sp. at different concentrations. YSA at 0.5 % was selected to be used during 30 min with live feed. The gilthead seabream larvae trial comprised one treatment where live feed was bathed with YSA vs. a Control (bathed with clear water) (each n = 4). Larval quality parameters (growth, survival, swimbladder inflation, body anomalies and caudal fin development), digestive capacity (digestive system histology and enzymatic activity), immune response (lysozyme activity and cortisol concentration) and microbiological parameters were monitored. Fish larvae from YSA exhibited higher growth rate than Control (P < 0.05). A higher food intake or a reduction of the bacterial load might justify this result. Still, lower survival rates were observed for YSA. This result might be related with variations of the bacterial community or/and to a possible ichthyotoxic effect of A. armata metabolites carried by the live feed. Treatment with YSA also influenced the whole body cortisol since lower concentrations were observed for this group. Further research on how cortisol mechanisms are affected is required to fully understand its effects. Seabream larvae from YSA exhibited lower number of bacteria, either for larvae ability to prevent or reduce the bacteria colonization, which can be related to an enhancement of larval fitness, or to the possibility that A. armata metabolites were carried to the larvae. The reduction of the bacterial load accomplished with live feed immersed for 30 min in YSA improved S. aurata larvae fitness, although the effects are not fully understood.