The present study was aimed to evaluate the moderating properties of Lavender (Lavandula
officinalis) essential oil (LEO) against immunotoxic effects of the organophosphate pesticide,
malathion in rainbow trout, Oncorhynchus mykiss. For this purpose, fish were supplemented with
LEO at dietary concentrations of 0.5, 1, 2 and 4 ml/kg diet LEO for 56 days. A non-LEO
supplemented group was also considered as control. After 57 days feeding trial, biochemicals
were assayed in the blood and kidney tissue and then fish exposed to a sub-lethal concentration
of malathion [0.24 mg/l equal to 30% of LC50 (0.8 mg/L)]. After 57 days feeding trial, the serum
total immunoglobulin, respiratory burst activity, lysozyme activity and complement activity
significantly elevated in fish treated with 1 and 2 ml LEO/kg diet compared to non-LEO
supplemented individuals (P<0.01). Such changes were not observed in non-LEO supplemented
fish (P>0.01). Significant elevations were observed in the expression of the immune genes
(iNOS and C3 genes) in fish treated with 0.2–2 mg LEO/kg diet compared to non-supplemented
ones (P<0.01). The lysozyme and complement activity significantly decreased in fish fed 4 ml/kg
diet (P<0.01). After exposure to malathion, all immune components significantly declined in
control and those treated with 0.5, 1 and 4 ml LEO/kg diet (P<0.01). In contrast, the immunity
components exhibited no significant changes in fish treated with 2 ml LEO/kg diet after exposure
(P>0.01). The expression of iNOS and C3 genes significantly reduced in control and fish fed 0.5,
1 and 4 ml LEO/kg diet in response to malathion (P<0.05). Furthermore, the expression of these
genes showed no significant changes in fish fed with 2 ml LEO/kg diet after exposure (P>0.01).
The findings of the present study suggested an immunoprotective role for dietary LEO at
optimized dietary concentrations of 1 and 2 ml LEO/kg diet against oxidative stress and toxicity
induced by malathion. Nevertheless, LEO at high dietary concentration (4 ml/kg diet) had
reducing effects on the fish immunity