Senegalese sole (Solea senegalensis) is one of the most promising species for Southern European aquaculture. However, control of opportunistic diseases caused by pathogens such as Tenacibaculum maritimum is a bottleneck for sole aquaculture. Such diseases are favoured by some current production conditions in intensive aquaculture such as high density, temperature fluctuations, fish handling, and their synergistic effects, which are capable of inducing a stress response. Nutrition has been shown to have a strong impact on fish health, in particular in what concerns immune competence and intestinal health. This lead to the concept of functional feeds which in already widely adopted in ongrowing fish operations but not so much in hatchery and nursery phases. Micro and macro -algae are rich in bioactive compounds with potential to increase robustness of early life stages of fish. The aim of this study was to evaluate the immune response of S. senegalensis postlarvae when fed microdiets fortified with different algae species, and their blends, are included as functional ingredients to boost immunocompetence and overall performance.
Two trials were conducted with Senegalese sole post-larvae were fed a Control diet, and the same diet fortified with 3% to 6% inclusion of micro and/or macro -algae. The trials started at 34 days after hatching (DAH) and lasted 4 weeks. Growth performance, survival, and whole-body immune response were assessed, as well as the expression of a panel of genes related with immune response (i.e., HAMP, complement C3, gLys, IL1b, IL10, TLR1 and TRL5). A follow-up trial was performed after the second trial to evaluate the capacity of post-larvae to cope with a Tenacibaculum maritimum infection inflicted by bath exposure.
The first trial indicated that biomasses of Nannochloropsis sp., Skeletonema sp. and Tetraselmis striata, improved the innate defence mechanisms in Senegalese sole, while Nannochloropsis also improved antioxidant capacity.
The second trial showed that a blend of Nannochloropsis sp., and Gracilaria gracilis enhanced growth performance of sole, as well as its innate defence mechanisms and antioxidant capacity. When challenged with T. maritimum sole responded with a 20% increase in survival when compared to the CTRL group, validating that algae blends inclusion in post-larvae microdiets improve immune competence of Senegalese sole post-larvae, and pave the way for the use of functional feeds in marine fish hatcheries.