The incorporation of natural ingredients that improve the immune system of fish has become increasingly recognised, and algae can be used as additives or food supplements in aquaculture due to their nutritional value, availability and low cost.
For this reason, scientists in Iran included different levels of the red algae (Laurencia caspica) in rainbow trout diets and evaluated its effects on the immune response when the fish were challenged with the pathogen Aeromonas hydrophila.
The trout were fed for eight weeks with diets that had different levels of an algae extract (0%, 0.5%, 1%, 1.5% and 2%). After this period, 10 specimens from each group were injected with the bacterium intraperitoneally and kept on the same diets for 10 more days.
The results indicated that the inclusion of the algae extract in the fish diet improved the relative expression of the IL-1β, lysozyme II, Complement C3 and TNFα genes.
“Based on the results, the relative expression of the genes tested showed significant increases in the 1.5% inclusion fed group compared to control groups,” the study authors noted.
Regarding mortality levels, the fish that were fed with the microalgae had a higher survival percentage than the control, with the inclusion level of 1.5% being the one with the highest percentage of surviving fish.
With these data, the researchers concluded that the immunological changes of rainbow trout can be improved by adding an extract of L. caspica to the diet.
“In accordance with the effective results of L. caspica extract on stimulating the immune system and increasing resistance of fish against A. hydrophila, it is recommended to use this algae extract in rainbow trout diets at a concentration 1.5%,” they said.
Read the study abstract titled “Effects of feeding with red algae (Laurencia caspica) hydroalcoholic extract on antioxidant defense, immune responses, and immune gene expression of kidney in rainbow trout (Oncorhynchus mykiss) infected with Aeromonas hydrophila” here.