Herbal Oil and Its Effects on Stress Levels in Fish

Jenn Hoskins
17th June, 2024

Herbal Oil and Its Effects on Stress Levels in Fish

Image Source: Natural Science News, 2024

Key Findings

  • The study by Akdeniz University evaluated oregano essential oil (OO) as an anaesthetic for Nile tilapia, comparing it to clove oil (CO)
  • OO at 60 mg/L was found to be an effective anaesthetic, similar in efficacy to CO
  • Both OO and CO initially increased glucose levels, indicating a common stress response
  • At 24 hours post-application, cortisol levels in fish treated with OO were lower than those in the control group, suggesting reduced long-term stress
Anaesthetics play a crucial role in aquaculture, facilitating various handling operations such as transportation, vaccination, grading, and sorting. A recent study conducted by Akdeniz University[1] evaluated the efficacy of oregano essential oil (OO) as an anaesthetic for Nile tilapia, comparing it to the commonly used clove oil (CO). This study aimed to determine the optimal concentration and assess the post-application stress effects of OO. The researchers exposed Nile tilapia juveniles to different concentrations of OO (20-100 mg/L) and CO (50 mg/L) to find the most effective dose and exposure time. After identifying the optimal concentration of OO, they analyzed stress parameters such as glucose and plasma cortisol levels at various intervals (0, 2, 6, 12, and 24 hours) post-application. These results were then compared to a control group and the CO group. The study found that OO, which contains over 78% carvacrol, was an efficient anaesthetic for Nile tilapia, with an effective concentration of 60 mg/L. The opercular beats (gill movements) of fish did not significantly differ between any concentration of OO and CO, indicating similar efficacy in immobilization. Basal glucose levels in blood without anaesthesia were recorded at 39.33 mg/dL, significantly lower than those observed at the first two sampling points (0 and 2 hours) for both OO and CO groups. This initial spike in glucose is a common stress response. Regarding plasma cortisol levels, the CO group exhibited a secondary stress response at 12 hours (17.91 ± 4.21 ng/mL). However, both OO and CO groups showed decreased cortisol levels at 24 hours post-application (7.13 ± 0.14 ng/mL and 7.01 ± 0.54 ng/mL, respectively), which were below the control group's cortisol concentration (12.28 ± 1.81 ng/mL). This suggests that OO may be effective in reducing long-term stress in fish. These findings align with previous research on the use of natural anaesthetics in aquaculture. For instance, clove oil has been widely used due to its effectiveness in immobilizing fish for various procedures[2]. However, improper use of clove oil can lead to decreased fish viability and distorted physiological data, emphasizing the need for proper training in its application[2]. Similarly, Alpinia galanga oil (AGO) has been shown to reduce stress in Nile tilapia during handling and transportation, with nearly normal levels of blood glucose and plasma cortisol[3]. This supports the potential of natural oils like OO as viable alternatives to traditional anaesthetics. The current study by Akdeniz University contributes to this body of knowledge by demonstrating that OO is not only effective but also potentially less stressful for fish compared to CO. This is particularly important as stress can significantly impact fish welfare and aquaculture productivity. Previous studies have highlighted the importance of considering stress from a psychological perspective rather than purely physiological[4]. Cortisol responses, although adaptive, can indicate how fish perceive their environment and their psychological well-being[4]. The reduction in cortisol levels observed with OO use suggests that it may be less distressing for fish, contributing to better overall welfare. In conclusion, the study provides valuable insights into the use of oregano essential oil as an anaesthetic in aquaculture. By reducing stress and potentially lowering mortality rates associated with traditional anaesthetics, OO could offer a more humane and effective solution for handling operations in fish farming. Further research is needed to evaluate its efficacy across different fish species and to determine optimal concentrations and exposure times.

HerbsHealthAnimal Science


Main Study

1) Effective concentration of herbal anaesthetics Origanum vulgare L. oil and its effects on stress parameters in Nile tilapia (Oreochromis niloticus).

Published 16th June, 2024


Related Studies

2) Effect of anaesthesia with clove oil in fish (review).


3) Effects of Alpinia galanga oil on anesthesia and stress reduction in Oreochromis niloticus.


4) Cortisol and finfish welfare.


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