Effects of dietary seaweed supplementation on hypoxia tolerance and oxidative stress response in gilthead sea bream (Sparus aurata)

Magnoni, Leonardo; Querioz, Augusto; Martos-Sitcha, Juan Antonio; Tromp, Kevin; Schrama, J.W.; Gonçalves, José; Calduch-Giner, Josep Alvar; Pérez-Sánchez, Jaume


Intensive aquaculture practices involve rearing fish at high densities in enclosed spaces, circumstances in which they may experience hypoxic events. Seaweeds (SW) and their derived compounds when included into fish diets may increase antioxidant defenses, improving welfare. The gilthead sea bream (Sparus aurata) has a growing importance in the European aquaculture sector. Thus, our aim was to evaluate the effect that dietary SW supplementation has on the metabolic profile and antioxidant capacity of sea bream juveniles subjected to an acute hypoxic event and ulterior recovery to normoxia. For this purpose, fish (105±2 g) were distributed into 24 tanks (60 L, 7 fish/tank) and fed for 34 days a commercial diet supplemented with Gracilaria sp. (+GR, 5%) or Ulva sp. (+UL, 5%), or without SW supplementation (Control). Fish were subjected to acute hypoxia (4 tanks/diet, 24h, DO 1.3mg/L) in a controlled system and sampled 24h after returning to normoxia (Hypoxia/Recovery). Another group remained in normoxia during the whole trial (4 tanks/diet, DO 8.6mg/L). Hypoxia produces an increase in the O2 carrying capacity in the fish, displayed by an increase in HCT values in all dietary groups, although the increase was most noticeable in the MC[Hb] of +GR and +UL treatments. At transcriptional level, a PCR-array of 29 selected genes in liver and heart showed differentially expressed markers related to oxidative stress, which improve oxidative capacity during normoxic and/or hypoxia/recovery conditions preferentially in those fish fed +GR diet. Such results are in accordance with the higher survival rates of fish fed +GR diet than of those fed a control diet (61±4% and 29±6%, respectively, P=0.017). Our results suggest that compounds with antioxidant properties in +GR diet may have a protective role during hypoxia. The nature of these compounds and possible mechanisms implied in the response are currently being investigated.