Alga diet formulation – An attempt to reduce oxidative stress during broodstock conditioning of Pacific oysters

• Published in: Aquaculture Vol. 500; pp. 540 - 549
• Main Authors: Amaro, Helena M., Rato, Ana, Matias, Domitília, Joaquim, Sandra, Machado, Jorge, Gonçalves, José F.M., Vaz-Pires, Paulo, Ozorio, Rodrigo O.A., Pereira, Luis F., Azevedo, Isabel C., Sousa-Pinto, Isabel, Catarina Guedes, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2019
• Subjects: Antioxidant; Crassostrea gigas; Macroalgae; Microalgae; Ulva rigida; Microalgae; Ulva rigida; Antioxidant; Crassostrea gigas; Macroalgae
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2018.10.060

The Pacific oyster Crassostrea gigas is among the most frequently cultured aquaculture species worldwide. In bivalve aquaculture, some environmental factors may induce the production of Reactive Species of Oxygen (ROS) that besides causing injuries to several vital cellular components, may lead to inflammatory processes. Usually, antioxidant enzymes of bivalves defense systems have an important role in the diminution of harmful effects of ROS. However sometimes it is not enough to restore the oxidative balance, being required an additional action of external antioxidant compounds. Knowing that biochemical composition of the diets may influence the physiology of bivalves, the aim of this study was to evaluate the effects of different ratios of microalgae and macroalgae on the oxidative stress responses during broodstock conditioning of C. gigas. Seven hundred and twenty oysters were divided in four dietary groups (3 tanks/diet; 60 oysters/tank). Each group was fed with one of the following diets: 100% macroalgae (Ulva rigida) (Diet 1); 50% macroalgae +50% live microalgae blend (Diet 2); 25% macroalgae +75% microalgae blend (Diet 3); or 100% microalgae blend (Diet 4). The microalgae blend comprised 33% Tisochrysis lutea and 66% diatoms (75% Skeletonema costatum + 25% Chaetoceros calcitrans). To assess diets effectiveness in the reduction of oysters oxidative stress, antioxidant capacity of the diets and the oxidative stress responses of the oysters were determined. The ABTS+, DPPH, ORAC, O2− and −NO assays were performed on diets to characterize their antioxidant capacity; Moreover, a possible anti-inflammatory effect of diets was assessed via human red blood cell (HRBC) membrane stabilization by heat induced assay. Catalase, lipid peroxidation, glutathione S-transferase and total and oxidized glutathione were quantified in the oysters to evaluate the dietary effects on the oxidative stress responses. Flesh weight of oysters fed Diet 3 and 4 was significantly higher than oysters fed with diets 1 and 2 (P ≤ .001). Results revealed that a 25% macroalgae and 75% microalgae blend (Diet 3) was the most effective dietary formulation in decreasing the oxidative stress, in terms of TG levels during the broodstock conditioning of the Pacific oysters, and in terms of NO and O2−; also exhibiting a potential anti-inflammatory effect. An additional advantage in supplementing 25% of Ulva rigida is the reduction of microalgae production costs during the broodstock conditioning of Pacific oysters. •Alternative diet formulation as a tool to reduce effects of oxidative stress in C. gigas oysters.•The inclusion of macroalgae Ulva at 25% of the diet showed to be effective in reducing the oxidative stress in oysters.•Macroalgae inclusion in oyster diets decrease the demand of microalgae and, the production costs of broodstock conditioning.