This study evaluates the effects of Cannabidiol (CBD) on the haematological parameters of acutely stressed and non-stressed Nile tilapia (Oreochromis niloticus, Linnaeus), reared in a recirculating aquaculture system. O. niloticus were fed with and without CBD (0, 0.001, 0.002 and 0.003% of feed weight) and with and without hydrocortisone (0 or 0.01% of body weight) for 72 hours. This experiment compared blood glucose, haematocrit and protein levels of the plasma of the fish. Among the non-stressed groups, fish fed with the highest concentration of CBD showed to have less stress in terms of the stress parameters, while the highest stress was detected in the stressed group supplemented with no CBD. No significant difference in stress was observed between the different concentrations of CBD supplementation of fish in a 72-hour period.