Aquaculture is considered a sustainable solution for the growing food demand of this century1. Within animal production, aquaculture is the sector that shows the fastest expansion rate, consistently increasing every year its share of the total seafood produced worldwide2. Despite the major technological investments made towards maximizing farmed seafood production and value, aquaculture has always had to face the double challenge of developing cost-effective aquafeeds that meet fish species (particularly, marine carnivorous ones) metabolic and nutritional requirements, while reducing as much as possible the use of meals and oils derived from wild fish, which raise strong ecological concerns and compromise oceans’ sustainability3. During the last year, the sector was further defied by the limited availability and escalating prices of raw materials (such as cereal/vegetable meals and oils) that came along with the war in Ukrania (2022). Hence, this has recently called for the urgent discovery of new alternative sources of nutrients that suit the nutritional and energetic demands of farmed fish and, thus, can potentially be used in aquafeeds’ formulations.
The inclusion of seaweeds has been pointed out as an eco-friendly strategy to naturally enrich the aquafeeds with specific nutrients that are essential, though deficient, in the human diet4,5. Still, the current knowledge is very limited in what concerns their nutraceutical/functional potential, as well as, the effective doses necessary to improve the welfare of farmed animals, often compromised by captivity, high rearing densities and disease outbreaks.
Hence, the present study aimed to explore the effectiveness of aquafeeds biofortified with a brown (Laminaria digitata) and a red (Asparagopsis taxiformis) macroalgae (at three inclusion percentages) in improving the antioxidant, metabolic and digestive performance of two juvenile farmed fish ecologically and commercially relevant within the Mediterranean setting - Sparus aurata and Diplodus sargus.
Material and methods
S. aurata and D. sargus juveniles with ~8 g of body weight (BW) were kept in recirculation aquaculture systems (RAS) under optimal development conditions (20ºC, > 7 mg/L O2). During the feeding trials, both fish species were fed ~2% of their BW with a commercial-based diet (CTR) and the S. aurata specimens with three experimental functional diets biofortified with 1.5%, 3% and 6% of L. digitata (whole, dried, and powdered) and the D. sargus specimens with three experimental diets supplemented with 1.5%, 3% and 6% of A. taxiformis (whole, dried, and powdered).
After 30 days of trial, 6 fish from each treatment and species were randomly collected and were euthanized for dissection and collection of muscle, gut and liver tissues.
To assess the effectiveness of biofortified aquafeeds to improve animal metabolism, digestive activity and overall welfare, the following physiological endpoints were assessed: oxidative stress (total antioxidant capacity [TAC], lipid peroxidation [LPO], superoxide dismutase activity [SOD], catalase activity [CAT] and glutathione S-transferases activity [GST]), metabolic enzymes activity (lactate dehydrogenase [LDH] and citrate synthase [CS]) and digestive enzymes activity (α-amylase, pepsin, trypsin and lipase)6. To normalize the results of each biomarker, total protein levels were also quantified according to the Bradford assay.
Results and Discussion
Data are still currently being analysed. Yet, preliminary results showed that aquafeeds biofortified with both studied macroalgae significantly modulated farmed S. aurata and D. sargus antioxidant, metabolic and digestive performance, especially at the highest inclusion rate (6%). Contrasting previous studies using dried macroalgae as feed additives, the present results seem very promising, evidencing that L.digitata and, especially, A. taxiformis can have a positive effect on the antioxidant and metabolic activity of farmed marine juvenile fish.
This work was supported by Fundação Portuguesa para a Ciência e Tecnologia (FCT I.P.), under the framework of the project Aqua-CLIMADAPT (PTDC/CTA-AMB/0592/2021). Isa Marmelo and Sofia Sousa also acknowledge FCT I.P. for their PhD grants (2020.04413.BD and 2022.12454.BD).
1Galappaththi, E. K., Ichien, S. T., Hyman, A. A., Aubrac, C. J., Ford, J. D., 2020. Climate change adaptation in aquaculture. Reviews in Aquaculture. 12(4), 2160-2176.
2FAO, IFAD, UNICEF, WFP and WHO., 2018. The State of Food Security and Nutrition in the World 2018. Building climate resilience for food security and nutrition. Rome, FAO. Licence: CC BY-NC-SA 3.0 IGO.
3Oliva-Teles, A., Enes, P., Peres, H., 2015. Replacing fishmeal and fish oil in industrial aquafeeds for carnivorous fish. Feed and feeding practices in aquaculture. 203-233.
4Castanho, S., Califano, G., Soares, F., Costa, R., Mata, L., Pousão-Ferreira, P., Ribeiro, L., 2017. The effect of live feeds bathed with the red seaweed Asparagopsis armata on the survival, growth and physiology status of Sparus aurata larvae. Fish physiology and biochemistry. 43, 1043-1054.
5Mota, C. S., Pinto, O., Sá, T., Ferreira, M., Delerue-Matos, C., Cabrita, A. R., Almeida, A., Abreu, H., Silva, J., Fonseca A. J., Valente, L.M., Maia, M. R., 2023. A commercial blend of macroalgae and microalgae promotes digestibility, growth performance and muscle nutritional value of European seabass (Dicentrarchus labrax L.) juveniles. Frontiers in Nutrition. 10, 570.
6Maulvault, A. L., Camacho, C., Barbosa, V., Alves, R., Anacleto, P., Pousão-Ferreira, P., Rosa, R., Marques, A., Diniz, M. S., 2019. Living in a multi-stressors environment: An integrated biomarker approach to assess the ecotoxicological response of meagre (Argyrosomus regius) to venlafaxine, warming and acidification. Environmental research. 169, 7-25.