Abstract

Fishes are now the second most used experimental animal across Europe and these important laboratory models are adopted across a variety of scientific disciplines. In order for research data to be meaningful and reliable, fish should be kept in good health and welfare prior to experimentation as well as during. Scientists have a legal obligation to monitor welfare ensuring animals are in optimal condition, but this is also useful to gauge the severity of the procedure and to decide when the severity has been exceeded and the animal requires euthanasia. This presentation will review a variety of methods to assess welfare in fishes including body condition scoring, general, behavioural and physiological indicators and the use of score sheets. Indicators can be divided into operational (conducted by the tank side) or laboratory where specialist software and laboratory equipment are required). Research on the behavioural responses to a variety of common invasive laboratory procedures will be presented as well as information on how to alleviate pain. If a fish is exhibiting severe changes or the responses exceed the permitted severity of a procedure, then euthanasia should be employed. The latest research findings on humanely ending the life of fishes will be discussed. 

Reference list: 

1. Sneddon LU, Schroeder P, Roque A, Finger-Baier K, Fleming A, Tinman S, et al. Pain management in zebrafish. Lab Anim. 2023;58:261–276.

2. Sneddon LU, Roques JAC. Pain recognition in fish. Vet Clin North Am Exot Anim Pract. 2023;26(1):1–10. doi:10.1016/j.cvex.2022.07.002.

3. Sneddon LU, Wolfenden DCC, Leach MC, Valentim AM, Steenbergen PJ, Bardine N, et al. Ample evidence for fish sentience and pain. Anim Sentience. 2018;3:17.

4. Sneddon LU. Pain perception in fish: indicators and endpoints. ILAR J. 2009;50(4):338–342.

5. Saarinen U, Sundell E, Sneddon L, Gräns A. Novel euthanasia technique for zebrafish using electric shock in standard group housing aquaria. Sci Rep. 2025;15(1):3011. doi:10.1038/s41598-025-87540-4 

Learning outcomes

• Explain why assessing fish welfare is vital for ethical, scientific and legislative reasons  

• Identify key welfare indicators in laboratory fish

• Have knowledge of body condition scoring and score sheets

• Distinguish operational vs laboratory-based assessments

• Understand the current state of the art with regards euthanasia of fishes