Utilization of Origanum oil as a health promoter in Nile tilapia (Oreochromis niloticus) challenged with Pseudomonas aeruginosa

This study investigated the potential immune-enhancing effects of Origanum oil on Nile tilapia (Oreochromis niloticus) under normal conditions and after a challenge with Pseudomonas aeruginosa. The fish were categorized as follows: not challenged and received no supplements; not challenged and received Origanum oil; challenged and not received any supplements; challenged and received florfenicol; challenged and received Origanum oil; challenged and received both Origanum oil and florfenicol. Origanum oil was administered at a dose of 10 mL/kg of diet for 28 days, and florfenicol at a dose of 10 mg/kg of fish weight after the challenge for a duration of 7 days. Origanum oil significantly aided florfenicol in reducing mortality and morbidity resulting from the challenge with P. aeruginosa. Fish that received Origanum oil alone demonstrated slight increases in proximate composition, including moisture, crude lipid, crude fiber, and crude ash, compared to those that did not undergo any administration or bacterial challenge. The total blood protein levels exhibited significant increases in the group that was not challenged and received Origanum oil and the group that was challenged and received both Origanum oil and florfenicol, following both linear and quadratic patterns. The latter group also showed significant increases in the levels of globulin. There was a notable variation in the total leukocytic count among the groups, with a discernible increase from group 1 to group 6 (in the same order as the groups mentioned above). It appeared that florfenicol maintained neutrophil and lymphocyte percentages in the challenged fish at levels similar to those not challenged and receiving no supplements. Meanwhile, Origanum oil seemed to increase neutrophil percentage and decrease lymphocyte percentage, either alone or when combined with florfenicol, whether in challenged or non-challenged fish. The fish that were challenged and received both Origanum oil and florfenicol showed the lowest serum levels of ALT, urea, and creatinine among the challenged groups. Necrosis was observed in the gills, hepatopancreas, spleen, intestine, and stomach in the group challenged with P. aeruginosa. However, these pathological changes were markedly not detected in the challenged fish that received Origanum oil, with only focal lesions in the hepatopancreas and intestine. Interestingly, the challenged fish that received both Origanum oil and florfenicol exhibited a normal histological