Anaesthesia of laboratory, aquaculture and ornamental fish: Proceedings of the first LASA-FVS Symposium

Abstract

Following on from the Annual Fish Veterinary Society Conference, this symposium was organised with the Laboratory Animal Science Association and brought together experts from ornamental (pond and aquarium) fish practice, aquaculture and aquatic-research facilities to discuss good practice of anaesthesia. This proceedings paper gives an overview of relevant experiences involving a range of immersion drugs including tricaine, benzocaine and isoeugenol, as well as a summary of the main topics of discussion. While fish anaesthesia is commonplace, administration methods, drugs and monitoring procedures may often be regarded as antiquated when compared with mammalian practice. These limitations notwithstanding, individual fish will benefit from good anaesthetic monitoring. Although the most common anaesthetic drugs may be perceived as equally efficacious and therefore interchangeable for different settings, challenges are different for the anaesthesia of grouped fish, when determining species-dependent anaesthetic dosing in a multi-species tank, or adapting to farming requirements, nationally licensed products, costs and withdrawal periods. The fish anaesthetic arsenal fails to address premedication, analgesia and issues of averseness. The two latter factors should be part of the evaluation of anaesthetic protocols; therefore, instructions for the analgesic provision of lidocaine to fin clipped zebrafish are proposed. Euthanasia practices could sometimes be refined too. Alternative physical methods such as electrical stunning are options to be considered.

A Multi-Site Assessment of Anesthetic Overdose, Hypothermic Shock, and Electrical Stunning as Methods of Euthanasia for Zebrafish (Danio rerio) Embryos and Larvae

“…The least effective treatment for the euthanasia of zebrafish embryos and larvae by overdose was buffered tricaine, with recovery rates after one hour immersion being close to that of control. This is particularly relevant considering that tricaine is widely used as a euthanasic agent for all developmental stages of fish [3,9,14,29]. However, similar results have been reported in other studies.…”

“…Considering that larvae can respond to aversive stimuli and display other signs of consciousness similar to adults before they reach regulatory protection [4][5][6][7], the use of anesthetics should be preferred to other chemical intoxicants, for which adverse effects are less known. However, the use of, for instance, tricaine for euthanasia raises the issue of the demonstrated averseness of the compound in adult zebrafish [8][9][10][11][12][13][14]. Larvae demonstrate more resistance to a tricaine overdose than fry or adults [8,15].…”

“…An ill-performed procedure would induce unnecessary harm and compromise animal welfare, data quality, and reproducibility. Euthanasia should induce the least distress possible in a controlled manner; it should result in either a fast loss of consciousness possibly spoiled by transitory averseness, or a slow but stress-free experience [14].…”

Screening of Anaesthetics in Adult Zebrafish (Danio rerio) for the Induction of Euthanasia by Overdose

“…The experiments were designed to replicate routine husbandry practices where fish are netted out of a housing tank and immersed into another tank containing the euthanasia solution. In gill breathers, drug administration by bath immersion is equivalent to inhaled drug administration in lung breathers [ 13 , 14 ]. In laboratories, the immersion bath is often not replaced after each euthanasia procedure but reused throughout the day.…”

“…Danio rerio is a small freshwater species and may not be susceptible to the same treatments as, for instance, a large marine species. This is not only true for physical methods but includes anaesthetic overdoses, as anaesthetic agents may cause differential effects in different species [ 13 , 14 , 15 ]. For instance, while 0.4 g/L lidocaine hydrochloride (HCl) irreversibly euthanized adult zebrafish [ 9 ], doses up to 0.8 g/L induced anaesthesia with full recovery in the similarly sized adult marine medaka ( Oryzias dancena ) [ 16 ].…”