Effects of feed supplemented with Lentinula edodes mushroom extract on the immune response of rainbow trout, Oncorhynchus mykiss, and disease resistance against Lactococcus garvieae

This research was conducted to determine the effects of Lentinula edodes (L. edodes) medicinal mushroom extract as a trout feed supplement on the immune response and disease resistance against Lactococcus garvieae in rainbow trout (Oncorhynchus mykiss). For this purpose, the fish were fed with 1% and 2% L. edodes mushroom extract supplemented diet for six weeks. During the trial, blood samples were taken from 10 fish/group each week up to 6 weeks. Furthermore, at the end of the trial, the fish were challenged with L. garvieae pathogen by intraperitoneal injection. Upon the evaluation of the results, feeding the rainbow trout with mushroom extract supplemented diet showed a significant influence on immunological parameters. The parameters were found to be higher in fish fed with the experimental diet than the control group. Statistically significant levels of serum total immunoglobulin were detected only in the fish group fed with 2% L. edodes mushroom extract supplemented diet. The maximum influence on immune response occurred in rainbow trout fed with 2% L. edodes extract. As a result of the challenge test, the survival rate was found to be the highest in the 2% L. edodes supplemented feeding group. The results suggested that a diet supplemented with L. edodes mushroom extract enhanced the immune response and decreased the mortality rate of rainbow trout against L. garvieae. Statement of relevance This study determined the effects of an edible mushroom extract on the immune system and resistance to disease in rainbow trout. The use of mushroom extract in fish diet protected rainbow trout partially from lactococcosis disease, increased their survival rate, and also enhanced their immune response. This experiment was performed in a commercial trout farm at the region therefore the application was found to be suitable for aquacultural fields.