Effects of the Na diformate and citric acid oral use on some skin mucosal immunity indices of rainbow trout (Oncorhynchus mykiss) following experimental challenge with Yersiniosis

The present study intends to assess the effects of Na diformate oral use with citric acid on some skin mucosal immunity indices (total protein, total immunoglobulin (TIg), lysozyme, protease, esterase, and alkaline phosphatase (ALP)) of rainbow trout following experimental challenge with Yersiniosis agent (Yersinia ruckeri). Subsequent to the determination of the 7-day median lethal dose (LD50) of Yersinia ruckeri, fish were stocked in eight groups and two repetitions. The acidifiers separately with a dose of 0.2%, and combined 0.1+0.1% was added to the commercial diet. Five days after inoculation, feeding of fish with acidifiers commenced, and following 15 days, the mucus samples were gathered from the skin of anesthetized fish to measure immune indices. Results showed that the 7-day LD50 of Y. ruckeri was 8.91×105 CFU/ml. In the main experiment, findings indicated the significant effect of Na diformate on the increased levels of mucoid total protein and proteolytic activity of healthy or diseased fish. The acidifiers-contained diet because of potentially having synergistic effect caused inducing the mucus TIg. It seems that the orally use of Na difirmate in 0.2% of the diet separately or combined with citric acid, at least for 15 days, can improve the cutaneous mucus immunological indices that its result is an increase in the survival rate of farmed rainbow trout.