I am a bit confused. I am planning an experiment in the field where fish will be caught by electrofishing. Afterwards, they are supposed to be euthanised by using an anaesthetic.
I found literature which recommended 2-Phenoxyethanol and linked it to a low cortisol response. A bit late I found papers that claimed the opposite. I used glove oil before and I thought that this option is also the most environmentally friendly one since I am working in the field. I would like to ask you about your opinion and your experience. I want to measure the Cortisol response in the blood afterwards and oxidative stress. Thank you in advance.
Anesthesia is performed in both inhaled and injected form in fish. In inhalation anesthesia, the anesthetic is added to a tank containing water that has the proper pH and oxygen. And the fish comes out of the water under anesthesia when it reaches the right level. There are two drugs in this category: tri-methane sulfate and processed essential oil of cloves. Sometimes inhalation anesthesia is not possible. For example, in some very large species, there is no space for an anesthesia tank or in the case of tuna, they can not be kept in captivity. It is done in the dorsolateral and in the back muscles up to the lateral line. But this method may not be ideal. Drugs in this category also include ketamine and propofol
Hi,
I think it was a good choice, some recommendations are available:
CCAC guidelines on: euthanasia of animals used in science
https://www.ccac.ca/Documents/Standards/Guidelines/Euthanasia.pdf
" 4.1.1.3 Immersion TMS is a recommended method for amphibians and fish; however, it is acidic and must be buffered (Cakir and Strauch, 2005). Use of immersion methods (such as TMS, benzocaine, etomidate, metomidate and clove oil) must be followed by a physical or chemical method to cause brain death. Immersion methods may be weak or ineffectual on fish which breath-hold or breathe air. "
Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to “Aspects of the biology and welfare of animals used for experimental and other scientific purposes” EFSA-Q-2004-105
https://ec.europa.eu/environment/chemicals/lab_animals/pdf/efsa_opinion.pdf
" Recommendations: The following methods cause a minimum of pain and distress: • Chilling in air • Chilling in ice/water slurry • Immersion in a clove oil bath "
Guidance for Industry Concerns Related to the use of Clove Oil as an Anesthetic for Fish
https://www.fda.gov/media/69954/download
Article Effects of Clove Oil as a Euthanasia Agent on Blood Collecti...
" Euthanasia with clove oil did not blunt the expected elevation of serum cortisol levels elicited by an acute premortem stress. According to our findings, clove oil is a fast-acting agent that minimizes the cortisol response to euthanasia in zebrafish and allows the collection of large volumes of blood postmortem. These results represent a significant refinement in euthanasia methods for zebrafish. "
Article Effects of anesthesia with MS-222, clove oil and CO2 on feed...
" Our results support previous findings that clove oil is a reasonable alternative to MS-222 "
Best regards
Tomasz
Hi
Working for along time on fish anesthesia, I could say ANESTHESIA INDUCE STRESS AND CORTISOL ELEVATION. But keep in mind longer induction time and higher anesthetic consentration, induce more severe stress. Cortisol response is time dependent, thus try to anesthetize the fish within a short time. You can reach deep anesthesia within 60 sec using clove oil and MS222. But such a short time does induce cortisol elevation. See my articles for more information.
If you catch the fish by electrofishing, they will be imobilized for a while. You can take blood within this period, fish the fish size and your skill are adequate. I sample the fish without anesthesia, sometimes, when I want to omit the stress caused by anesthesia. But it needs exprience.
Other suggestion is to use metomidate for anesthesia. This anesthetic blocks cortisol response, although the fish are stressed.
Good luck
Ps.
If you want to assay long term effects of environmental stressors on fish, cortisol is not a suitable choise as cortisol exhibites a sharp short term response, but decrease after that. Measuring antioxidant enzymes, TBARS, serum protein fractions, ions ... are better ones
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