Survival, Growth, and Antioxidant Response in Vaccinated Oncorhynchus mykiss Fed Hypericum

This study evaluated the antimicrobial, immunostimulatory, antioxidant enzyme activity and growth promoting effects of Hypericum perforatum oil as a feed additive in rainbow trout (Oncorhynchus mykiss) vaccinated against Lactococcus garvieae. Experimental diets included a Control group, vaccinated group and treatment group (1.5 mL/kg oil). The trial was conducted in triplicate, with 50 fish per 400 L tank over 8 weeks. At the start of the trial, fish were vaccinated intraperitoneally with inactivated L. garvieae. After feeding trials, fish were challenged with the pathogen, and mortality rates, relative survival percentage, and growth performance metrics were evaluated. The control group exhibited 52.50% mortality, whereas the vaccinated group supplemented with 1.5 mL/kg oil achieved 100% relative survival percentage. In this study, it was observed that the highest antioxidant enzyme activities were found in the unvaccinated and pathogen-infected control groups, while the vaccinated and vaccinated + essential oil groups showed lower antioxidant enzyme activities. It was determined that the unvaccinated groups produced excessive reactive oxygen species in their cellular metabolism. Additionally, significant improvements were observed in final weight, feed conversion ratio, and survival rates, indicating that Hypericum perforatum oil enhances both disease resistance and growth in rainbow trout.