SULPHATED POLYSACCHARIDES EXTRACTED FROM SEAWEED ON SKIN-MUCUS IMMUNITY OF RAINBOW TROUT

In pursuing a more sustainable aquaculture the prevention of disease becomes an important goal. Skin-associated lymphoid tissue (SALT) has the mucus as the most significant innate response mechanism. Due to this effect of mucus, pathogens are immobilized before they can adhere to or make contact with epithelial cells. Interest in the use of marine macroalgae in animal production is increasing, mainly due to the wide range of biological activities attributed to it, such as immunomodulatory, antioxidant and antiviral properties. Using the vast sustainable marine resources of the coast of Brittany (France) and in collaboration with several research bodies, Olmix has been able to isolate, identify and concentrate sulphated polysaccharides from the cell wall of macroalgae that have different activities to support the general health of animals. Some of these isolated polysaccharides include activities such as immunomodulation, mucin secretion and the strengthening of intestinal barrier functions.

The study was carried out at indoor race-way system of a commercial fish farm located in São Paulo Brazil for 11 weeks (78 days). Fish were assigned to 2 treatments with 2 replicates (100 fish/tank), totalizing 400 fish. Two iso-nutritive diets, Control and Test (commercial product based on combination of green and read algal extracts), were formulated to differ only on the inclusion of 0.3% of macroalgae polysaccharides. Fish were fed twice daily at 9:00 am and 4:00 pm ad libitum. Average water temperature and dissolved oxygen were 14 °C and 7,3 mg/L, respectively. Skin mucus samples were collected at week 4 and 11. The functional activity of complement was assessed by hemolytic assays (n=8/treatment) using sheep red blood cells as targets. Mucus samples (50 μL) were incubated at room temperature for 25 min with 2% sheep blood (25 μL), cold-PBS (75 μL), the supernatant was collected, and absorbance read at 405 nm. Lysozyme activity was determined in skin mucus (n=8/treatment) using a turbidimetric method incubating 10 μL mucus sample in 200 μL suspension of Micrococcus lysodeikticus in PBS (0.2 g/L) at pH 6.8, absorbance read at 450 nm. Rainbow trout weight were at day 1: 89.8 g ±1.9g, at week 4: 189.2 g ±6.1 and at week 11: 338.5 g ±7.5. Hemolytic activity was improved in macroalgal sulphated polysaccharide fed trout and increased at week 11 compared to week 4 for both groups. Lysozyme activity was not significant affected neither treatment of sampling week. These results highlight the potential effects of macroalgal sulphated polysaccharides on improving the innate immune response of skin-mucus in rainbow trout.