Effects of safflower (Carthamus tinctorius) extract on serum antibacterial activity of rainbow trout (Oncorhynchus mykiss) against Aeromonas hydrophila, Streptococcus iniae and Yersinia ruckeri

In the present study, the effects of safflower (Carthamus tinctorius) extract on serum antibacterial activity of rainbow trout (Oncorhynchus mykiss) against Aeromonas hydrophila, Streptococcus iniae and Yersinia ruckeri was studied. In this regard, 450 fish with average weight of 100±10 g were stocked into fifteen fiberglass tanks. This experiment consisted of 3 treatment groups (received 50, 100 and 200 mg/kg BW safflower extract via IP injection), one positive control group (just received normal saline) and one negative control group (with no injection). Blood samples were taken at the 3th, 7th and 10th days after the injections, and antibacterial activity of serum were determined in vitro using CFU method. The results showed that safflower extract injection had no significant effects on serum anti-bacterial activity against A. hydrophyla and Y. rukeri during 10 days post injection. However, in the fish receiving 100 mg/kg safflower extract, serum bactericidal activity against S. iniae was significantly higher than the other groups. This study demonstrated that safflower extract at the doses of 50-200 mg/kg via IP injection did not cause significant changes in serum antibacterial activity against A. hydrophila and Y. ruckeri, but injection of 100 mg/kg extract led to an increase in the serum antibacterial activity against S. iniae, in rainbow trout.