Nile tilapia is a species with high tolerance to stressful conditions induced by super-intensive rearing systems. One of the dangers of these systems is the high ammonia water concentrations that led to low growth rate, feed efficiency and survival. Dietary supplementation of herbal essential oils is recommended for aquatic animals due to their growth-promoting, immune and antioxidative potential.

A team of researchers evaluated the feed inclusion of menthol essential oil from 0.1 – 0.4% on growth performance, digestive enzyme activity, immunity and antioxidative responses in Nile tilapia. After eight weeks, fish were exposed to acute ammonia challenge.

Researchers found that the optimum rate of dietary menthol essential oil required for the best growth is 0.26% and 0.30%. Dietary menthol enhanced the protease activity while lipase and amylase activities were influenced. Before and after the ammonia challenge, lysozyme, phagocytic activities, phagocytic index, superoxide dismutase, catalase and glutathione peroxidase were higher in fish fed menthol than fish fed menthol-free diet. On the other hand, cortisol, glucose, and malondialdehyde were decreased by dietary menthol.

Ammonia stress induced a reduced lysozyme, phagocytic activity and phagocytic index but increased the superoxide dismutase, catalase, glutathione peroxidase, malondialdehyde, cortisol and glucose levels. The related inflammatory genes were reduced by dietary menthol either before or after the ammonia exposure, and the mRNA levels of these genes were increased after ammonia stress.

“Menthol essential oil inclusion at the rate of 0.22% to 0.30% is recommended to increase the growth performance, protease activity, immunity, antioxidative response and the resistance against ammonia exposure in Nile tilapia,” researchers said.

Download the study here.