Dietary administration of microalgae Navicula sp. affects immune status and gene expression of gilthead seabream (Sparus aurata)

Effects of silage microalgae enriched with a probiotic and lyophilized microalgae were evaluated on main immune parameters and different gene expression of gilthead seabream (Sparus aurata L.). A total of 60 seabream were grouped into 3 treatment diets which were a control diet (commercial diet) without microalgae (C), commercial diet supplemented with silage microalgae Navicula sp. plus Lactobacillus sakei 5-4 (106 CFU g−1) (SM), and commercial diet supplemented with lyophilized microalgae (LM) for 4 weeks. Generally, the results showed a significant increase in the immune parameters, principally in leucocyte peroxidase, phagocytosis and complement activities in fish fed with SM diet compared to control group. About the gene expression in head-kidney, transcript levels (Interleukin-8, Interleukin-1β and β-defensin) were upregulated in fish fed with SM after 4 weeks of treatments. However, the gene expression was upregulated in intestine from fish fed with LM with significant difference in transferrin and cyclooxygenase 2 gene at 2 weeks, and in occludin, transferrin, interleukin-8 and interleukin-1β at 4 weeks. Finally, about the digestive enzymes, LM diet caused an upregulated of α-amylase and alkaline phosphatase genes at 2 weeks; however SM diet caused an upregulated trypsin gene at 4 weeks. SM diet a higher enhancing effect on gilthead seabream immune parameters than that observed when using LM. Furthermore, dietary administration of microalgae Navicula sp. provokes upregulation of several genes in the gut that correlates with slight inflammation. Further studies are needed to know if this diatom could be useful for administering as diet supplement for farmed fish.