Introduction
Aquaculture plays a pivotal role in guaranteeing food security in a world with a fast-growing population. Thus, in recent years, there was a need to increase and intensify the production of aquatic organisms and consequently, applied research led to advances on the optimal farming conditions for several species. With a view to continue improving the performance and sustainability of the aquaculture industry it is now necessary to fine-tune aquaculture practices, aquafeeds, methodologies and analytics. This integrated vision will allow for a more precise and efficient management of resources, improving fish health, growth rates, and overall production.
One of the important steps that has been taken to increase sustainability of the sector and to reduce the impact of aquaculture on marine ecosystems was the inclusion of ingredients of vegetable origin in fish diets. In this regard, the inclusion of macro and microalgae extracts has been explored, particularly because of the bioactive compounds these ingredients contain.
The main objective of this work was to evaluate the impact of algae biomasses and extracts, on overall performance and resilience of gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax) post-larvae, using a multidisciplinary analytical approach.
Experimental trial
Algae extracts were prepared by GreenCoLab and incorporated into aquafeeds by SPAROS, Lda. Fish trials were conducted at the Aquaculture Research Station facilities (EPPO/IPMA) and analytics performed by EPPO/IPMA and S2AQUAcoLAB.
Fish trials were divided in two phases:
1) 33-35 days after hatching (DAH) post-larvae, obtained from EPPO/IPMA broodstock, were fed four different feeds: Winfast (commercial control diet, SPAROS Lda.), BLEND1, BLEND2, and BLEND3 (three diets with different inclusion of micro- and macro-algae extracts). Fish were fed respective diets for 1 week, where they changed to a control feed for a second week, and then back to the functional feeds for another week. Fish were sampled at that point (S1) for growth and survival assessment and effects of the different blends in gene expression and oxidative stress enzymes’ activity.
2) At 57-58DAH all fish groups were fed a boost diet for 1 week (BLEND6). BLEND2 was eliminated to give place to a CTRL group that did not receive a boost diet. Fish were sampled previously to stress exposure (S2) to evaluate the boost diet effects.
3) After, larvae were subjected to a stress event (air exposure) and to a challenge test, with a pathogenic bacteria, Photobacterium damselae subsp. piscicida. Survival was recorded and samples were collected between 6-24h hours after exposure (S3) for gene expression analysis and oxidative stress enzymes’ activity.
Results and Conclusions
At the end of trial 1 (S1), the post-larvae fed with diets containing micro- and macro-algae showed no differences in growth. Although not significant, a higher fish survival was observed in the fish fed with the BLEND diets. Regarding gene expression, an increase in stress-related genes, such as GPX1 and GPX4, was observed in all BLENDS when compared to CTRL, in seabream larvae. In S2, the addition of a boost diet (BLEND 6) decreased the expression of antioxidant enzymes to control levels (S2 vs S1). After the stress event (S3), the addition of a boost diet (BLEND 6) increased the expression of antioxidant enzymes such as GPX1 and GPX4, in a dose dependent manner. These results suggest that in the early stages, the performance of fish larvae might benefit by the incorporation of micro- and macro-algae in the diets.
Acknowledgements
This study was funded by PACTO DE INOVAÇÃO BIOECONOMIA AZUL (Project No. C644915664-00000026), AQUARAS (MAR- 02.01.02-FEAMP-0223) and SAUDE&AQUA (MAR 02.05.01-FEAMP-0009). The technical assistance of EPPO and S2AQUAcoLAB staff was highly appreciated throughout the study.